Figure 2.

This pictorial representation shows the types of circadian rhythm sleep disorders (CRSDs) in humans which arise due to the phase alteration of the circadian clock.

From the top, the first representation shows normal entrained sleep/wake cycle (~24h) synchronized to the environment (LD cycle). In ASPS patients, the sleep phase is advanced than the conventional sleep time and individuals go to bed early and wake early in the early morning. In DSPS patients, the phase of the sleep is rather delayed and in both these disorders, patients have difficulties in synchronizing their activities to the social schedule of the society. In non-24 h circadian rhythm disorder, the patient’s rest/activity cycle is delayed every day and this results in sleep onset problems and persisting sleepiness during daytime. In subjects with shift work disorder, individuals work during the night, which is the circadian time designated, for sleep and consumption of food, and exposed to light at an inappropriate time (e.g. LAN; Light At Night). This abnormal behavioral disorder leads to impairment in cognition, attention, and sleep. Moreover, they are prone to work-related injuries, road, and occupational accidents. When individuals travel to a different time zone, circadian clock takes some time to adjust to the new time schedule. Until the adjustment of the clock, individuals have difficulties in getting sleep and other behavioral activities leading to jet lag. In irregular sleep-wake disorder, the patients exhibit a characteristic lack of unconsolidated sleep/wake pattern and possess at least three bouts of sleep.