2.1. Participants
mental illness, psychotic episodes, anxiety, hypomania, depression
RECRUITMENT
Subjects were recruited via digital (social networks and mailing) means in September 2020 and were asked to complete the PSQI to select participants with low sleep quality (target population). The inclusion criteria were: (i) having a PSQI score of >5, indicating impaired sleep quality, and (ii) not suffering from severe anxiety or depression, severe mental illness (e.g., hypomania or psychotic episodes), or any other diagnosed mental or physical health condition at the time of recruitment. This second criterion was checked by directly asking the participant about their condition.Eligible participants signed an informed consent and privacy policy and were randomly assigned to an intervention or control group, using a simple randomization procedure with a 1:1 allocation ratio, by using the R package randomize. Subjects in the passive control group, for ethical reasons, were offered the same intervention as the treatment group once the study was completed. The study was registered retrospectively in the ISRCTN registry (ISRCTN39530091). 