Circadian Rhythm Sleep-Wake Disorders
Delayed and advanced phase
Delayed sleep phase disorder is common in adolescents: sleep onset and wake times are later than desired, with normal sleep when allowed to follow the internal clock. Advanced sleep phase disorder occurs in older adults with early bedtime and early awakening. Diagnosis uses sleep diaries and actigraphy; dim-light melatonin onset can help.
Shift work and jet lag
Shift work disorder causes insomnia or sleepiness related to work schedules. Jet lag follows rapid travel across time zones. Management includes timed light exposure, melatonin (taken at the appropriate local time), and schedule adjustment.
Non-24-hour rhythm
Non-24-hour sleep-wake rhythm disorder is common in blind individuals because light entrainment is lost; melatonin can help.
Traps
Do not confuse delayed phase with insomnia; the key is whether sleep is normal when the schedule is free. Melatonin timing matters: taken too early or late it shifts the clock the wrong way. Light exposure in the evening worsens delayed phase.
Rule of thumb: For delayed sleep phase, use morning bright light plus evening melatonin; for advanced phase, use evening light and morning melatonin.