Circadian rhythm sleep-wake disorders — structured clinical viva

You are the psychiatry registrar. A 42-year-old night-shift nurse has insomnia when trying to sleep by day, microsleeps on the drive home, and residual depression. A 19-year-old university student in the same clinic falls asleep at 04:00 and skips morning labs but sleeps well in semester break until noon. Discuss CRSWD classification, mechanisms (SCN, two-process, PRC), discriminators from insomnia and mania, assessment tools, and evidence-based management for DSWPD and shift-work disorder including melatonin timing and modafinil evidence.