Effect of Darkness Retreat on Worry and Rumination in a Non-clinical Population: a Pilot Study
Phase: NA
Conditions: Study Protocol Feasibility, Non Clinical Anxiety, Non Clinical Worry, Non Clinical Rumination
Sponsor: University of Social Sciences and Humanities, Warsaw

Document date: 19.02.2026 
 
 
 
 
 
 
 
 
 
 
 
Study title: Effects of darkness retreat 
 
 
Study protocol and statistical analysis plan 
 
 
 
 
 
 
 
 
NCT number: Pending 
 
 
 
 
 
 
 
 
 
 

1. Study protocol 
Background 
 
The Dark Retreat (DR) experience is a practice originating in the tantric movement of 
Tibetan Buddhism, in which a person stays in total darkness for a few days - eating, 
sleeping, meditating without any contact with natural or artificial light (Lowenthal, 
2003). Historically reserved for Tibetan monks, it is now gaining popularity among 
people seeking spiritual experiences. According to proponents, the retreat is meant to 
allow the body and mind to relax, to take a closer look at oneself, and consequently to 
break strenuous cognitive or emotional habits, as opposed to under conditions 
opposite to the overstimulation of the outside world.  
 
The Youtube channel features posted interviews with Dark Retreat participants, 
in 
which 
they 
talk 
about 
their 
retreat 
experience 
(https://www.youtube.com/@skycaveretreats). In support of this study, a content 
analysis of the recordings was conducted to identify co-occurring themes in the 
interviews. Findings from the above analysis indicate that participants experienced a 
change in their perceptions of themselves, their relationships with others, their 
thinking, or their emotional experiences. Each participant described the dark retreat 
experience as deeply spiritual, life-transforming and positively impacting their mental 
health. A meta-analysis conducted by Karki et al. (2024) based on an international 
sample from eight countries indicated that religiosity and, to a lesser extent, 
spirituality are associated with mental health. It remains an open question whether 
the experience of darkness promotes the development of spirituality or otherwise 
affects mental health?  
 
To our knowledge, the phenomenon of dark retreat has not previously been of 
interest to psychologists. Testimonies of participants indicate that perhaps deprivation 
under controlled conditions can be associated with positive changes in psychological 
functioning. However, there are no studies defining what this change could be or what 
is also a possible explanation for its process. The following study will be the first 
attempt to observe, in psychological terms, the experiences of dark retreat 
practitioners and, if we can observe differences before and after the experience, to 
answer the question of whether these changes persist over time. Analysis of the DR 
testimony recordings allowed us to pick out the following variables relating to various 
manifestations of mental health - anxiety, mindfulness, meaning in life, growth, 
emotion regulation and concentration. Due to the lack of available literature data 
relating to dark retreats, the following review of the current state of knowledge relates 

to mindfulness research. This selection was dictated by the thematic overlap between 
DR's statements and the principles of Mindfulness (Kabat-Zinn, 2015 ) 
 
Experiencing excessive anxiety and often accompanying worry are among the 
common mental health problems (Haller et al., 2014; Momin et al., 2023) although of 
lesser severity they can occur in the healthy population (Clancy et al., 2020; Dupuy et 
al., 2001). For people with anxiety disorders, the recommended treatment of choice is 
psychotherapy, which is assessed to be highly effective and persistent over time 
(Curtiss et al, 2021; Johnco et al, 2024; Kowalski et al, 2024). Individuals looking to 
reduce their anxiety, excessive feelings of stress or worry can also benefit from other 
alternative, non-pharmaceutical methods with proven efficacy, such as practicing yoga 
or mindfulness methods (Crane et al., 2021). For example, practicing yoga has been 
proven to reduce perceived levels of stress and anxiety (Erdoğan Yüce and Muz, 2020). 
Preliminary findings also indicate that yoga may be effective as either an adjunct to 
therapy or as a stand-alone treatment for patients with anxiety disorders (Nemeroff 
et al., 2024; O'Shea et al., 2023). Mindfulness training, on the other hand, unlike yoga, 
which is based on body-directed mindfulness practice, focuses on learning to direct 
one's attention to the present moment in such a way as to not judge but accept one's 
own emotional or cognitive experiences (Kabat-Zinn, 2015). Thus, mindfulness 
practice can lead to a change in the perception of internal experiences, and by 
extension also change the way we think and the emotions that arise as a result of 
thoughts, for example, anxiety (de Abreu Costa et al., 2018). A meta-analysis by 
Shumer et al. (2018) also indicated that practicing mindfulness may be associated with 
reduced negative reactivity in response to external and internal experiences. 
Mindfulness can either be treated as a trait, referring to an innate ability to be mindful, 
or developed as mindfulness practice continues (Bamber and Schneider, 2016). 
Mindfulness as a trait is associated with greater self-confidence, mental health, better 
emotion regulation, and correlates negatively with perceived life stress, anxiety and 
depression (Mesmer-Magnus et al., 2017). Hence,  need to create and evaluate 
training that promotes the development and enhancement of this trait is not 
surprising (Bayot et al., 2024, Bohlmeijer et al., 2010, Teasdale et al., 2016). From the 
accounts of dark retreat practitioners, it appears that retreat and sensory deprivation 
allowed them to observe their own thoughts related to past or present functioning 
and accept them. Therefore, we would like to verify whether the experience of 
darkness promotes the development of mindfulness and a change in severity of 
anxiety or worry.  
 
Practicing mindfulness can also promote positive changes in relation to mental 
health (Lindsay and Creswell, 2015). For example, a meta-analysis by Chu and Mak 
(2019) indicated that mindfulness-based interventions can increase a sense of 

meaning in life, although the effect was found to be moderate. A sense of meaning, 
defined as a state of self-knowledge about one's own meaning, purpose or significance 
gained in life (Kossakowska et al., 2013), is associated with better physical health and 
an overall sense of physical and psychological well-being, as well as lower anxiety (Chu 
and Mak, 2019). Preliminary findings also indicate that a consequence of mindfulness 
training may also be growth, although these studies refer only to post-traumatic 
growth (Post-traumatic growth, PTG; Shyiko et al., 2017), understood as a process of 
change after a traumatic experience in the following areas: appreciation of life, 
interpersonal relationships, recognition of personal strengths, openness to taking a 
different life and spiritual path (Tedeschi and Blevins, 2015). Although current 
concepts refer to growth after very difficult and stressful events, opinions are 
beginning to emerge in the scientific literature that not only the worst but also the 
best experiences can lead to lasting beneficial changes, known as post-traumatic 
growth (Mangelsdorf et al., 2018). It is believed that mindfulness, may be associated 
with mental health benefits, as it allows for the regulation of affective states and meta-
awareness of one's experiences, which may consequently lead to a different 
interpretation of events or better coping with difficult situations (Lindsay and Creswell, 
2016). Given the numerous testimonies of reevaluating the lives of darkness retreat 
participants, we would like therefore to examine whether growth and changes in 
meaning in life can be observed among darkness retreat participants.   
 
Some studies also suggest that mindfulness training can improve cognitive 
function, both in young adults and children ( Bauer et al., 2020; Kittler et al., 2022), 
although the findings are inconclusive. For example, a meta-analysis by Gill et al. 
(2020) found no effects on attention and executive functioning as a result of 
mindfulness practice, while other studies have indicated training effects on inhibition 
and task shifting (Williams et al., 2024). Despite the outlined inconsistencies, in the 
proposed study we have also decided to test whether the experience of darkness 
would be associated with changes in cognitive functioning. It should be emphasized, 
however, that if persistent changes could be observed, there is no explanatory model 
based on the current state of knowledge regarding the effects of mindfulness on 
cognitive function.  
 
When analyzing the potential of a given experience, training or therapy, it is 
also important to control for variables on the part of the participant or patient that 
may increase the likelihood of change. In the context of psychotherapy, it has been 
noted that readiness to change, understood as the degree to which a person is willing 
to accept, adopt and enforce a specific plan to change the status quo (Rafferty et al., 
2012), has been shown to be related to therapy outcomes (Krebs et al., 2018). Other 
factors that may also be associated with the final outcomes of therapeutic 

interventions include: expectations of therapy (Kuusisto et al., 2011), credibility of 
psychotherapy (Kumpasoğlu et al., 2024) and the need to pay for the service, although 
opinions are divided regarding the relationship between payment and the 
effectiveness of psychotherapy (Herron and Sitkowski, 1986). In our study, we also 
plan to control for the above factors on the part of darkness retreat participants, in 
order to assess their impact on the outcome of the experience.  
Feasibility and Pilot Study Goals 
 
1. Is the protocol feasible, implementable, and safe under real-world conditions 
when working with a non-clinical population? 
2.  Does a darkness retreat experience result in reduced levels of anxiety, 
negative affect, worry, and rumination, along with greater positive changes in 
psychological functioning—especially in attention, mindfulness, cognitive 
flexibility, emotion regulation, and a sense of meaning in life? 
3. If positive changes in psychological functioning are observed, are these 
changes less pronounced in participants undergoing high vs low monitoring 
conditions, i.e. three vs one psychological consultations per day? 
4. If positive changes in psychological functioning are observed, will they be 
lasting—that is, will they be maintained for six months after the experience 
ends? 
5.  Do individual traits, such as readiness for change and expectations regarding 
the experience, modify the immediate effects of participating in a darkness 
retreat? 
6. Does client satisfaction with intervention moderate the effects of participating 
in a darkness retreat? 
Hypotheses 
1. The primary goal of our study is to verify if the designed protocol is practical, 
implementable, and safe in real-world conditions when working with a non-clinical 
population. Our basic hypothesis is that these protocols will fulfill this assumption 
regardless of the chosen condition (more frequent vs less frequent check ins).  
2. There will be a significant decrease in the levels of anxiety, negative affect, worry, 
and rumination, as well as in positive changes in mental functioning (attention, 

inhibition, mindfulness, cognitive flexibility, emotion regulation, and a sense of 
meaning in life) among individuals undergoing a darkness retreat. 
3. Considering that a participant in a retreat needs time for internal exploration, we 
hypothesize that the protocol with standard (less frequent) psychological 
consultations will be more effective with regard to the improvements defined in H2 
compared to the protocol with enhanced (more frequent) consultations.  
4. At the follow-up assessment, changes defined in H2 and the hypothesized group 
differences (h3) will be stably observed. 
5. Individual characteristics, such as readiness to change and expectations regarding 
the experience, measured immediately before the intervention, will moderate the 
immediate effects of the darkness retreat. 
6. Client satisfaction and subjective ratings of the experience’s impact, measured 
immediately after the intervention, will moderate the long-term effects of the 
darkness retreat (at follow-up). 
Procedure 
Recruitment stage 
Participants will be recruited among university students through a two-stage 
process.  
Stage I 
Individuals expressing interest in participating in the study will first be asked to 
confirm that they are not currently undergoing psychotherapy or coaching, are not 
taking psychotropic medication, and are in generally good physical health. 
The following exclusion criteria will apply: 
diagnosed acute or chronic somatic illness (e.g., cardiovascular diseases); psychiatric 
or neurological disorders (e.g., depression, addiction, bipolar disorder, schizophrenia, 
epilepsy, stroke, traumatic brain injury, Parkinson’s disease, Alzheimer’s disease, or 
other forms of dementia); active suicidal ideation with plan or intent; current use of 
psychotropic medication; and pregnancy. 
Initial verification of the above criteria will be conducted through a screening 
questionnaire containing demographic questions and items regarding 
psychotherapy/coaching, psychotropic medication use, somatic health, suicidal 

ideation, pregnancy, and any lifetime diagnoses of behavioral or psychiatric 
disorders, including psychotic disorders, eating disorders, obsessive-compulsive 
disorder, substance use disorders, bipolar disorder. The screening will also include 
the following self-report questionnaires (using their Polish adaptations): 
● PSWQ: Inclusion criteria based on the PSWQ (Penn State Worry 
Questionnaire, Meyer et al., 1990.): 
To be considered for participation, individuals must obtain a total score 
between 40 and 80, i.e. moderate or high level of worry.In cases where 
participants fall within the high range (>60), if clinical levels of worry are 
identified during the clinical interview, they will be excluded from 
participation. 
● PHQ-9 (Spitzer et al., 1999) : Scores above 10 will be interpreted as elevated 
risk of depression; individuals scoring 20 or more will not be invited to the 
clinical interview. 
 
● GAD-7 (Spitzer at al., 2007): Scores of 7 or more will be considered indicative 
of elevated generalized anxiety symptoms; individuals scoring 15 or more will 
be excluded from further participation. 
 
● AUDIT (WHO, 2001): A score above 8 will indicate increased risk of 
problematic drinking; individuals scoring 22 or more will not be invited to the 
clinical interview. 
 
● DUDIT (WHO, 2001): A score above 4 will be interpreted as elevated risk of 
substance use; individuals scoring 7 or more will be excluded from the study. 
 
The questionnaire will also include the following DSM-5-based screening tools (APA, 
2013), which will not lead to automatic exclusion. However, results exceeding the 
following thresholds will require in-depth assessment during the clinical interview: 
● DSM-5 – Panic Disorder: score ≥ 26 
 
● DSM-5 – Social Anxiety Disorder: score ≥ 26 
 
● DSM-5 – Post-Traumatic Stress Disorder (PTSD): score > 22 
 

STAGE II  
To exclude personality disorders, a two-step procedure will be implemented. First, 
participants will complete the Personality Belief Questionnaire (PBQ; Beck & Beck, 
1991) approximately one week before the scheduled interview; an elevated intensity 
of certain dysfunctional beliefs may indicate a possible personality profile. This will 
then be verified by a psychologist during the clinical interview using the Structured 
Clinical Interview for DSM-5 Personality Disorders (SCID-5-PD; First et al., 2016). 
Additionally, in order to exclude other mental health disorders (e.g., anxiety 
disorders, substance use disorders, claustrophobia, or PTSD), the psychologist will 
use the MINI measure (M.I.N.I. 5.0.0; Sheehan et al., 1998). 
Participants who complete the psychological interview—regardless of their final 
qualification for the study—will receive a compensation of approximately 200 ZŁ in 
shopping vouchers (50EUR).  
Ethical considerations 
The research procedure was submitted for evaluation by the Commission for Ethics 
in Empirical Research Involving Human Participants at SWPS University. All 
modifications to the original study protocol have been conducted in strict accordance 
with the guidelines of the SWPS University Ethics Committee. The project received 
formal approval (No. 2025 - 288) and all subsequent procedural updates were 
officially authorized under amendment aneks_2025-288.  
Participants 
The study sample will consist of 20-30 students aged 30-50. Eligible participants will 
be characterized as high-worrying (> 1 SD above the mean in PSWQ), yet classified as 
psychologically healthy based on screening and clinical interview results. 
All participants will be assigned to one of two experimental subgroups, both of which 
will undergo the darkness retreat condition. The groups will differ in the frequency 
and structure of psychological monitoring during the retreat: 
● Group 1 will follow low frequency monitoring with the standard consultation 
schedule established by the standard consultation schedule will follow the 
protocol established by the Within – The Ultimate Darkness Retreat team 
(the study’s host facility and sponsor) in Wróblewo, Poland. Monitoring will 

occur once per day in conjunction with meal delivery. 
 
● Group 2 will receive high frequency monitoring, i.e. psychological check-ins, 
suggested at regular 3-hour intervals during waking hours. This approach aims 
to increase psychological safety and allow for more robust, time-sensitive data 
collection throughout the retreat experience. 
Participants who enter the cabin will receive a compensation of 900 PLN in shopping 
vouchers (approximately 210 EUR). This payment will be provided regardless of 
whether they complete the entire experiment or choose to withdraw at any point. 
Additionally, they will receive 400 PLN in shopping vouchers (~100 EUR) for 
completing follow-up questionnaires six months after the retreat experience. 
Study Design and Methodology 
● Intervention Model (Parallel Assignment): The study is conducted at a 
specialized facility in Wróblewo, Poland, which has five available darkness 
cabins. Participants are organized into "slots" of five people per session. 
Within each slot, two intervention groups (High Frequency Monitoring vs. Low 
Frequency Monitoring) run in parallel. Due to the facility's capacity, the groups 
are distributed in a 2:3 or 3:2 ratio, and this distribution alternates with each 
subsequent slot to ensure balance across the study. 
● Allocation (Randomized/Pseudo-randomization): Participants are assigned to 
one of two groups (High vs. Low Frequency Monitoring) via block 
randomization. To maintain optimal monitoring standards within the facility’s 
capacity, an alternating 2:3 or 3:2 allocation ratio is applied across four 
dedicated session slots. Group assignment is revealed to participants 
immediately following the completion of the first wave of questionnaires 
(baseline), prior to the start of the retreat. 
● Masking (None / Open Label with Limited Initial Disclosure): This study is 
primarily open-label; however, a degree of limited disclosure is used during 
the recruitment phase to minimize expectancy bias. During initial screening, 
participants are informed they are applying for a "retreat study" focused on 
psychological well-being. They are not initially informed about the darkness 
component or the specific monitoring frequency. Detailed information about 
the darkness retreat is provided only after successful qualification. Full 
unmasking regarding the study's primary scientific objective (feasibility and 
protocol testing) will occur after the final follow-up assessment. 

● Informed Consent and Decision Process: The participation decision is a multi-
stage process. Potential participants first express interest based on general 
information. After the recruitment and qualification phase, they receive 
comprehensive details about the darkness retreat and the monitoring 
conditions, at which point they make a definitive decision to participate. The 
formal Informed Consent Form (ICF) is physically signed on-site at the facility 
in Wróblewo before the intervention begins.  
Individuals who meet the eligibility criteria will be informed about the specific nature 
of the intervention (darkness retreat). After confirming their willingness to proceed, 
participants complete the baseline assessments (Wave 1). All baseline assessments 
but one are completed 3 days (Friday)  before coming to the research  facility in 
Wróblewo (Monday). For legal reasons, the State-Trait Anxiety Inventory (STAI) must 
be completed in person in hard copy upon arrival at the research facility. 
Following these assessments (Wave 1), participants are assigned via 
pseudorandomization to one of two conditions: either low or high frequency of 
monitoring via psychological consultations. Subsequently, on the day of assignment, 
participants receive an email notification informing them of the specific condition to 
which they have been allocated 
Study Facility and Participant Support 
The study will be conducted at Within – The Ultimate Darkness Retreat, located in 
Wróblewo (the designated facility).  All accommodation and meals during the study 
will be fully covered by the organizers. 
To ensure participant safety, a psychologist (supervisor) will be appointed to monitor 
participants through scheduled psychological consultations (available at high or low 
frequency) and provide emergency support if needed. To minimize researcher bias, 
the appointed supervisor will have no prior experience with the darkness retreat. 
Study Phase I: Pre-arrival Assessment 
Three days before the scheduled arrival, participants will receive a set of online 
questionnaires to complete (using their Polish adaptations where applicable). This 
first wave of assessment focuses on the following measures: 
1. Negative Affect Measures: 
● Ruminative Thoughts Questionnaire (Baryła & Wojciszke, 2005) 

● Penn State Worry Questionnaire (PSWQ; Meyer et al., 199;) 
● CESD-R (Radloff, 1977) 
● STAI (Spielberger et al., 2011) 
2. Positive Mental Health Measures: 
● Abbreviated version of the Five-Facet Mindfulness Questionnaire 
(Bohlmeijer, et al., 2011) 
● Meaning in Life Questionnaire (MLQ; Steger at al., 2006) 
● Self-Compassion Scale – Short Form (SCS-SF; Raes i in., 2006) 
● Heart Rate Variability (HRV) 
3. Cognitive Functioning Tests: 
● Behavioral go/no-go tests 
4. Controlled Variables: 
● Personal Development Initiative Scale (Borowa et al., 2020) 
● Credibility/Expectations Questionnaire (Devilly & Borkovec, 2000) 
5. Physiological Monitoring: Participants in both groups will be equipped with 
WHOOP wristbands – wearable devices designed to monitor physiological activity. 
These wristbands will serve a dual purpose: from a research perspective, they will 
provide access to biological data such as circadian rhythm patterns and heart rate 
variability (HRV), offering deeper insights into the physiological processes 
accompanying the darkness retreat experience. From a safety perspective, they will 
enable real-time monitoring of participants’ condition, supporting one of the main 
goals of the pilot study: ensuring participant safety while assessing the feasibility of 
the proposed research procedure. 
Day 1 (Arrival & Preparation) 
 On arrival (Monday afternoon), participants will be welcomed and given a tour of 
the facility by their supervisor on site. 
● Participants will first read the informed consent form, which will then be 
discussed with a Supervisor. After this discussion, participants will sign the 
document before proceeding. In the following step, participants will complete 
the State-Trait Anxiety Inventory (STAI) on-site. Subsequently, the Supervisor 
will then discuss the course of the first two days at the facility Subsequently, 

and then they will participate in a brief one-on-one mindfulness training 
session.  
● Participants will be then shown the darkness cabins  
● Those who agree to participate  will then spend a trial night in the assigned 
cabin, exiting the next morning. 
Day 2 (After the trial night) 
● The next day, they will meet with the supervisor to discuss their initial 
experiences and confirm or decline further participation. 
● Participants attend provided meal, and rest.  
 
Days 2–5 (Main Experiment in Retreat Conditions) 
● Participants will enter the darkness cabin after group breakfast around 11 of 
the second day and remain there until around 11 AM the morning of the fifth 
day. 
● They will have no access to mobile phones, laptops, or watches. 
● Meals will be provided without direct interaction with others. 
● Participants will be free to leave the cabin at any time and may seek 
assistance from the supervisor if needed. 
● Depending on their assigned condition, participants staying in the darkness 
retreat cabin will undergo standardized interviews conducted by a supervisor 
during the retreat. The frequency and structure of these interviews will differ 
based on group allocation (low vs high frequency monitoring (i.e. 
psychological consultation) group), but all interviews will follow a predefined 
protocol to ensure consistency and participant safety. 
Post-Study Assessments (Exit Measures in Wróblewo) 
Upon completion of the retreat (day 5), participants will be asked to complete the 
same set of questionnaires/tests as described above (points 1–4) and additionally:  
●  Post-Traumatic Growth Inventory (PTGI) (PTGI; Tedeschi & Calhoun, 1996); 
●  Negative Effects of Intervention Questionnaire (NEQ; Rozental et al., 2016, 
2019)  
●  Client Satisfaction Questionnaire (Larsen et al., 1979). 

After assessments participants who wish to do so will have the opportunity to 
discuss their experiences with the study supervisor (The Supervisor uses only 
basic helping tools, such as paraphrasing and reflecting). 
Six-Month Follow-Up 
To assess the long-term persistence of observed changes, participants in all groups 
will complete the following questionnaires: 
● Ruminative Thoughts Questionnaire (Barilla & Wojciszke, 2005) 
● Penn State Worry Questionnaire (PSWQ; Meyer et al., 1990) 
● CESD-R (Radloff, 1977) 
● Go/no-go behavioral tests 
● Abbreviated version of the Five-Facet Mindfulness Questionnaire (Bohlmeijer 
et al., 2011) 
● Meaning in Life Questionnaire (MLQ; Steger et al., 2006) 
● Self-Compassion Scale – Short Form (SCS-SF; Raes et al., 2011) 
● Post-Traumatic Growth Inventory (PTGI; Tedeschi & Calhoun, 1996) 
● Personal Development Initiative Scale (Borowa et al., 2020) 
● Credibility/Expectations Questionnaire (Devilly & Borkovec, 2000)  
● Negative Effects of Intervention Questionnaire (NEQ; Rozental et al., 2016, 
2019)  
Following the follow-up assessment, participants will receive a personalized email 
explaining the study's true objectives and the necessity of initial limited disclosure to 
maintain scientific integrity. The communication will include a PDF debriefing form 
with instructions for withdrawing data and a link to an online survey to confirm 
understanding or request a meeting with the research team. Every participant 
retains the right to have their data permanently deleted and can schedule a private 
online consultation with a psychologist to discuss their experience. 
 
 
 
 
 

2. Statistical analysis plan 
2.1. General Analytic Strategy 
• 
Statistical analyses for primary and secondary outcomes will be performed 
using Linear Mixed-Effects Models (LMM). 
• 
LMM was chosen to account for the hierarchical structure of the longitudinal 
data (observations nested within participants) and to handle unbalanced data 
without ad-hoc imputation. 
• 
Parameters will be estimated using the Full Information Maximum Likelihood 
(FIML) method. 
• 
Analyses will follow both Intention-to-Treat (ITT) and Per-Protocol (PP) 
approaches. 
2.2. Model Specification and Hypothesis Testing 
The core model will include Time (Baseline, Post-intervention, 6-month Follow-up), 
Group (High vs. Low Monitoring), and the Group × Time interaction as fixed effects. 
A random intercept for each participant will be included to account for individual 
baseline variability. 
• 
Testing Intervention Efficacy (H2): Evaluated via the Main Effect of Time. A 
significant reduction in scores (e.g., PSWQ, STAI) or increase in positive 
functioning (e.g., FFMQ, MLQ) from Baseline to Post-intervention will support 
the efficacy of the Dark Retreat. 
• 
Testing Group Differences (H3): Evaluated via the Group × Time interaction. 
We hypothesize that the standard (low-frequency) monitoring group will show 
greater improvements compared to the high-frequency group. 
• 
Testing Long-term Stability (H4): Evaluated via planned contrasts comparing 
6-month Follow-up to Baseline. Stability is confirmed if the Follow-up scores 
remain significantly improved relative to Baseline. 
2.3. Outcome Measures Classification 
• 
Primary Outcome:  
o Pathological worry: Measured by the Penn State Worry Questionnaire 
(PSWQ). 
o Study Protocol Feasibility: Measured by objective recruitment and 
retention metrics, specifically: 
Completion Rate: Percentage of participants who complete the full 5-
day dark retreat. 

Retention Rate: Percentage of participants who complete the 6-month 
follow-up assessment. 
Safety: Incidence of emergency consultations and reports of adverse 
distress levels. 
• 
Secondary Outcomes: 
o Emotional Distress: STAI-Trait, CESD-R, and Ruminative Thoughts 
Questionnaire (RTQ). 
o Cognitive Performance: Attention/Cognitive Stability (Omission Errors 
and Reaction Time Variability (RTV)), and Inhibition (Commission 
Errors) derived from the Go/No-Go task. 
o Positive Mental Functioning: Mindfulness (Five-Facet Mindfulness 
Questionnaire, FFMQ), Meaning in Life (Meaning in Life Questionnaire, 
MLQ), Post-Traumatic Growth (Post-Traumatic Growth Inventory, 
PTGI), and Emotion Regulation (Heart Rate Variability, HRV and Self-
Compassion Scale – Short Form, SCS-SF). 
2.4. Statistical Rigor and Assumptions 
• 
Multiple Comparisons: The Benjamini-Hochberg False Discovery Rate (FDR) 
correction will be applied to all secondary outcome analyses to control for 
Type I error inflation. 
• 
Assumptions: Normality and homoscedasticity of residuals will be verified. 
Skewed cognitive (RT, RTV) or physiological (HRV) data will be log-transformed 
prior to analysis. 
• 
Missing Data: Handled via the LMM framework under the Missing at Random 
(MAR) assumption. 
2.5 Moderation and Exploratory Analyses 
To address H5 and H6, individual traits (Readiness to Change and Expectations 
assessed at pre-treatment and Satisfaction assessed at post-treatment) will be 
entered as continuous moderators into the LMMs. Due to the pilot nature of the 
study (N=20), these analyses will be treated as exploratory. 
2.6. Feasibility and Safety (H1) 
The feasibility of the study protocol, defined as a primary outcome, will be assessed 
using the following descriptive metrics and pre-defined benchmarks:  
• 
Recruitment Feasibility: Measured by the time required to fill each study slot 
(target: <3 months per 5-person cohort).  

• 
Retention and Completion: Assessed by the completion rate of the 5-day 
retreat (target: >80%) and the retention rate at the 6-month follow-up (target: 
>70%).  
• 
Adherence: Defined as the degree to which participants follow the 
intervention schedule, with a protocol deviation threshold of no more than 
one-hour delay in psychological consultations.  
• 
Data Completeness: Evaluated by the percentage of successfully collected 
self-report, behavioral, and physiological (HRV) data.  
• 
Safety and Adverse Events: Monitored through the incidence of emergency 
psychological support requests (target: ≤2 per session slot) and post-
intervention distress reporting.