Phenomenological Explorations of the Esketamine-Induced Transient Dissociative State

Ketamine is an anaesthetic used in low doses to treat depressive disorders. A related molecule, Esketamine, has recently been launched on the market for the treatment of resistant depression. One of the side effects of ketamine, like Esketamine, is induction of transient dissociative state. Dissociation has been described as disruption in continuity of conscious thought and emotion, cognitive processes disorganisation and an alteration in self-perception and environment perception. A study of healthy volunteers receiving ketamine showed that this state was manifested by altered sensory perceptions, with increased noise sensitivity, visual distortions and altered time perception. Few studies have looked at this phenomenon in the Esketamine context. However, it is a frequent side effect. With ketamine, it has been shown that anxiety associated with dissociative experience reduces the antidepressant effect. Benzodiazepines use for anxiolytic purposes is also thought to limit the antidepressant effect.

It is necessary to explore the Esketamine induced transient dissociative state in order to clarify this state and develop therapeutic strategies. The investigators have chosen a phenomenological approach, which is the only way to evaluate consciousness contents and structures, in order to explore this state using the experiential phenomenological interview.

Patients will be identified when they come for an Esketamine session performed as part of routine practice in the Psychiatry Department of Hôpital Sainte Musse. The clinician, who is also the study investigator, will then select patients who meet the protocol's inclusion criteria and inform them of the research before administering the Esketamine. He will explain the study in detail and give them the information letter.

Patients will then be seen again in consultation outside the Esketamine sessions, as part of routine practice, within a minimum of 48 hours. During this consultation, the investigating physician will obtain their oral consent to their participation in the research, resulting in a research consultation lasting around 45 minutes and including :

* an audio recording of an Experiential Phenomenological Interview;
* completion of the EQFC "Trait" questionnaire.

Eligibility Criteria:
Inclusion Criteria:

* Patient followed in the Psychiatry Department of Hôpital Sainte Musse, with depressive state characterized by the DSM-V criteria and treated with Esketamine between 2 days and 3 months prior to the study;
* Patient over the age of 18;
* Patient presented transient dissociative state during Esketamine treatment;
* Patient able to express his/her consent prior to participation in the study;
* Patient who understands and speaks French.

Exclusion Criteria:

* Patient with major anxiety and panic attack during an Esketamine-induced dissociative state, regardless of Esketamine effect;
* Patient under judicial protection (guardianship, curatorship...) or safeguard of justice;
* Pregnant, parturient or breast-feeding women;
* Any other reason that, in the opinion of the investigator, would interfere with the evaluation of the study objectives.