Fig. 2

Main steps followed in recruiting and working with volunteers during study stage 2. Interested participants are phone screened, and if screening positive, an initial appointment is scheduled to discuss in full detail the parameters of the study and answer any queries. During that appointment, a detailed screening process would take place. If participants are still eligible and willing to participate, signed informed consent is obtained. Additionally, as part of the screening process, participants need to give a urine sample to test for drugs of abuse and undergo an initial anatomical magnetic resonance (MR) scan. If still eligible, the dates for the conduction of the three study arms are arranged. The order of treatment arm allocation is random and unknown to the volunteers and the study investigators. This is determined by an external authority and takes place prior to the start of arm 1. Interventions during the three study arms were designed and validated during the previous study stage. Each of the three arms takes place with a temporal distance from the previous one of at least two weeks (*). EMA: ecological momentary assessment, ETB: emotional test battery, EPST: emotion potentiated startle test, LD: last study day, LSEQ: Leeds Sleep Evaluation Questionnaire, MRI: magnetic resonance imaging, RAP: randomisation phase, WP: wash-out period