Searches covered January 1990 through March 2025 and used combinations of sleep-related terms (e.g., insomnia, sleep disturbance, REM sleep, circadian rhythm), psychiatric disorder terms (depression, bipolar disorder, anxiety, PTSD, schizophrenia, ADHD, autism spectrum disorder, substance use), mechanistic terms (HPA axis, inflammation, orexin, neurocircuitry), and treatment-related terms (CBT-I, chronotherapy, IPSRT, melatonin, orexin antagonists). Here, HCRT is linked to major depressive disorder.