Nightmares are repeated extremely dysphoric and well-remembered dreams, which typically occur during REM sleep in the second half of sleep (late in the night or during the early morning hours) and upon awakening, individuals quickly become oriented, alert, and conscious of their surroundings. Standard definitions for nightmares often include awakening as an essential criterion, though research suggests that this is not always the case and not all researchers have adopted this waking criterion. Furthermore, although most nightmares occur during REM sleep, they can also occur during non-Rem sleep. Nightmares are very common in psychiatric populations. Studies have found nightmare prevalence rates of 28.4% and 17.5% in depression, 15.6% in anxiety disorders, 24.4% to 25.6% in drug or alcohol abuse, 60% to 90% in Posttraumatic stress disorder (PTSD), and 48% in psychotic disorders. Furthermore, since nightmares often do awaken the individual during the sleep cycle and can make returning to sleep difficult, nightmares can have indirect negative effects through sleep deprivation, which can lead to impaired attention, alertness, reaction time, cognitive processing capacity, memory, mood, ability to stay awake, and heightened pain sensitivity. However, nightmares can also have direct and specific effects. They can affect daily functioning and overall well-being. These implications are even more pronounced in individuals with mental health disorders, where negative outcomes of nightmares were found to often be independent of the co-morbid mental disorders. In psychiatric disorders, nightmares can function as a risk factor, a symptom, and as an exacerbating factor regarding psychiatric symptoms. Nightmares were also found to be significantly associated with higher risk of suicidal ideation, suicide, repeat suicide attempts, and death by suicide, often after controlling for co-morbid mental and other sleep disorders. One cognitive-behavioral-oriented treatment for nightmares is called Imagery Rehearsal Therapy (IRT). IRT asks patients to identify an especially distressing (possibly recurrent) nightmare and works together with the patient on changing the nightmare to a more positive theme, story line, or ending. The new contents are then rehearsed using imagery techniques. In IRT the nightmare can be changed in any way. Some authors argue that imagery rescripting may improve the perceived mastery over nightmares by providing a form of coping by rescripting them. Some authors Arntz speculate that imagery rescripting might modify the fear memory, leading to a reconsolidation with a new meaning that no longer prompts a strong fear response. Imagery rescripting might change the meaning of the original images and the associated automatic emotional processes. Since exposure is not considered to be the most important component of IRT, some authors have pointed out, that the new dream narrative does not have to include material from the original disturbing dream, where solution-oriented thinking may be triggered. IRT is currently among the most studied psychological approaches and is often recommended by guidelines with moderate to large effect sizes. IRT has been shown to be effective for the reduction of nightmare frequency, intensity, and distress. Effects have also been found on depression, anxiety, PTSD symptom severity, sleep quality, insomnia symptoms, and potentially on suicidal ideation. IRT has been used successfully for the treatment of posttraumatic and idiopathic nightmares with sexual assault victims with PTSD, war veterans with PTSD, psychiatric outpatients with various disorders, such as personality disorders, mood disorders, anxiety disorders, and PTSD, and with patients experiencing symptoms of psychosis. Studies have found long-term effects of IRT at follow-ups of 3, 6, 9 and up to 30 months.

To the knowledge of the investigators, there is no randomized controlled trial (RCT), which has investigated the efficacy of IRT in psychiatric inpatients. In order to design the most effective treatment protocol for nightmares, it is necessary to find what works for whom, and how it works. Thus, the proposed project aims to investigate the efficacy of IRT in an RCT with psychiatric inpatients with various disorders. The primary research question is whether IRT has a positive effect on nightmares of psychiatric inpatients in terms of frequency, distress, and intensity, which constitute the outcomes typically used to assess nightmares. A secondary research question is if certain nightmare characteristics and / or treatment characteristics moderate treatment efficacy.

For this study, sixty inpatients with nightmares will be recruited from the inpatient units of the PUK for an RCT. Prior to the first session, patients' electronic files will be screened for inclusion and exclusion criteria and to document medical information, such as current primary diagnoses and current medication. Participants will be randomly assigned to an IRT group or a TAU control group. T0: The first session will consist of informed consent and a first set of self-report questionnaires and interviews, which will assess demographic and personal information, primary psychiatric diagnoses, symptom severity of primary psychiatric diagnoses, psychotherapy motivation and hopefulness, nightmare frequency, nightmare distress, nightmare effects, nightmare content, overall sleep quality, and dream experiences and believes. At the end of the session, both groups will receive a dream diary, which they will fill out for each night for 4 consecutive weeks. The diary will measure nightmare frequency, nightmare distress, nightmare intensity, nightmare content, and if and for how long patients did their imagery exercises.T1: One week later, patients will hand in the completed questionnaires and the IRT group will receive a short IRT intervention. During the IRT session, the therapist will fill out a short questionnaire assessing characteristics of the imagery rescription session. The control group will receive a session in which potential problems with the dream diary will be discussed. Patients in the IRT group will be instructed to use imagery exercises for 10 to 15 minutes a day for the rest of the study period.T2: One week after the IRT or control session, patients will receive self-report questionnaires, which will assess symptom severity of primary psychiatric diagnoses, psychotherapy motivation and hopefulness, nightmare frequency, nightmare distress, nightmare effects, nightmare content, overall sleep quality, and dream experiences and believes. Patients of the IRT group will have the opportunity to ask questions about their treatment. T3: One week later, patients will hand in the completed questionnaires and they will receive the same questionnaires to fill out again. Additionally, patients will receive a questionnaire assessing whether and for how long patients did their imagery exercises during the study period. Patients will also hand in their dream diaries. A week later the questionnaires and dream diaries will be collected. Each patient will receive participant reimbursement of 30 Swiss francs (CHF) for their participation in the study. Furthermore, after data is collected, each patients from the control group will be offered an IRT session.