What is circadian rhythm sleep-wake disorder and name two common subtypes?

• A. Misalignment between circadian timing and environment; subtypes include shift-work type and jet-lag type.
• B. Excessive daytime sleepiness with REM onset; subtypes include narcolepsy and REM sleep behavior disorder.
• C. Difficulty maintaining sleep due to hyperarousal; subtypes include delayed sleep onset and early morning awakening forms.
• D. Sleep-wake cycle is normal; subtypes include insomnia and restless legs.

Answer: (A)

Circadian rhythm sleep-wake disorders come from the body's internal clock being out of sync with the outside world, so sleep and wake times don’t align with environmental cues like light and dark. When this clock-environment mismatch happens, people have trouble falling asleep or staying asleep, or they feel excessively sleepy during the day.

The option that best fits this concept notes that the problem is a misalignment between circadian timing and the environment, and it names two common subtypes: shift-work type and jet-lag type. Shift-work type occurs when work schedules keep you awake during your biological night, forcing daytime sleep and causing repeated misalignment. Jet-lag type happens after rapid travel across time zones, when the internal clock roughly 24 hours but is reset at incompatible times with the destination, producing insomnia and daytime sleepiness until re-entrainment occurs.

The other descriptions point to different sleep disorders: narcolepsy or REM sleep behavior disorder involve abnormal sleep states or daytime sleepiness not driven by circadian misalignment; hyperarousal-related insomnia focuses on trouble staying asleep for reasons other than clock timing; and saying the sleep-wake cycle is normal contradicts the very idea of a circadian rhythm sleep-wake disorder.