Non-24 hour sleep-wake rhythm disorder (Q41263)

Non-24 hour sleep-wake rhythm disorder is characterised by periods of insomnia and/or daytime sleepiness, alternating with periods of relatively normal sleep, due to a lack of entrainment of the circadian clock to the 24-hour environmental cycle. The period length of the circadian/sleep-wake cycle is typically longer than 24 hours. Symptoms occur as the circadian-controlled sleep-wake propensity cycles in and out of phase with the environmental day-night cycle. The disorder is seen most commonly in individuals with complete blindness. The symptoms should have persisted for at least several months and result in significant distress or mental, physical, social, occupational or academic impairment.