WELT-REST: WELT Randomized Evaluation of Sleep Therapy

Inclusion Criteria: * Adult patients ≥18 years old * Confirmed current diagnosis of F51.0 Nonorganic insomnia or G47.0 Sleep disorders * Possession of a mobile device with internet connection (must be run on iOS software, minimum version 18) with internet connection * Sufficient German language proficiency required for the correct use of the intervention and the mobile device * Personal e-mail address for registration * Willing and able to provide written informed consent * Insomnia Severity Index (ISI) socre of 15 or higher, indicating clinically relevant symptoms of insomnia * Registered with a GP, sleep specialist or other health care professional Exclusion Criteria: * Use of a digital interventioan for insomnia treatment in the past 6 months or planned use of comparable digital intervention during the study period * PHQ-9 score at screening ≥ 20 and/or item 9 f PHQ-9 ≥ 1 * GAD-7 score at screening ≥ 15 * Intermittent use and/or recent initiation (\< 3m) or planned use of insomnia specific prescription-only pharmacological therapy * Intermittent use and/or recent initiation (\< 3m) or planned use of a psychotropic during the study period which has recognised potential effects on insomnia * Participation in CBT or other psychotherapy to treat sleep disorders in the last 6 months (outpatient, inpatient) or planned start during the study period * Known history or diagnosis of substance or alchol abuse or dependence within 12 months prior to screening (diagnosis of F10-F19, excluding F17.1 and F17.2) * Current or planned participation in other clinical trials during the study period * Working in shifts * Currently pregnant or planning to become pregnant within the next 3 months * Any surgical procedure that was scheduled, planned, or conducted within the timeframe of the study (minor outpatient procedures under local anaesthetic or with no anesthetic are permitted) * Diagnosis of epilepsy * Presence of serious mental illness, such as (schizophrenia F 20.-, acute transient psychotic disorders F23.-, active manic episode F30.-, bipolar disorder F31.-, severe depression F32.3, F33.3) * Other diseases (such as acute or severe cardiac diseases, acute or severe respiratory diseases, acute or severe gastrointestinal diseases), conditions or therapies which, in the opinion of the investigator, could confound the study results or contraindicate participation. * Acute suicidal thoughts or intentions within the past 12 months * Presence of obstructive sleep apnea, restless legs syndrome, parasomnia, and other sleep behavior problem