Circadian Rhythm Abnormalities

It is thought that DSPS is caused by an insufficient ability to reset the sleep/wake cycle in response to environmental time cues - perhaps the biological clocks of DSP individuals have an unusually long cycle, or perhaps they are not sensitive enough to time cues.

There are other circadian rhythm disorders:

DSPS has in some instances followed an illness or head injury, and might run in families. But in most cases, it is not known what causes the biological clock to be confused. Because DSPS was discovered only in 1981, and there is little awareness of the disorder, it is difficult to get a reliable estimate of how widespread DSPS is. About 7% of adolescents have DSPS, and it is probably responsible for 7 -10% of cases of chronic insomnia.