Types of circadian rhythm disorders

Extrinsic type

Two of these disorders are extrinsic (from Latin extrinsecus, from without, on the outside) or circumstantial:

 Jet lag, which affects people who travel across several time zones. Seen in people who travel across time zones, symptoms include excessive sleepiness and a lack of daytime alertness.

§  Shift work sleep disorder, which affects people who work nights or rotating shifts. This sleep disorder affects people who frequently rotate shifts or work at night.

 Intrinsic type

Four of them are intrinsic (from Latin intrinsecus, on the inside, inwardly), "built-in":

§  Delayed sleep phase syndrome (DSPS), characterized by a much later than normal timing of sleep onset and offset and a period of peak alertness in the middle of the night.

§  Advanced sleep phase syndrome (ASPS), characterized by difficulty staying awake in the evening and staying asleep in the morning.

§  Non-24-hour sleep-wake syndrome (Non-24), in which the affected individual's sleep occurs later and later each day, with the period of peak alertness also continuously moving around the clock from day to day.

§  Irregular sleep-wake rhythm which presents as sleeping at very irregular times, and usually more than once per day (waking frequently during the night and taking naps during the day) but with total time asleep typical for the person's age.