Information on Sleep Disorders
(Adapted from the International Classification of Sleep Disorders,  American Academy of Sleep Medicine  2006.)

CIRCADIAN RHYTHM

Circadian rhythm sleep disorder, delayed sleep phase type – An individual with delayed sleep phase typically has difficulty initiating sleep at the desired time. If allowed to fall asleep and wake up at their preferred time, the bedtime tends to be later than would otherwise be preferred. Attempts to fall asleep earlier are difficult or impossible and waking at a required time is often difficult. This disorder is very common during adolescence.

Circadian rhythm sleep disorder, advanced sleep phase type – These individuals generally experience sleepiness in the late afternoon and evening hours. They tend to go to bed early and often awaken between 2 and 5AM.

Circadian rhythm sleep disorder, irregular sleep-wake type – Individuals with this disorder have no clearly defined sleep-wake rhythm or regular schedule of sleep. The wake and sleep periods are spread throughout the 24 hour day.

Circadian rhythm sleep disorder, free running type (non-entrained type) – The intrinsic circadian rhythm is longer than a 24 hour day and therefore bedtime and wakeup time tend to drift later each day.

Circadian rhythm sleep disorder, jet lag type – There is a temporary mismatch between the intrinsic circadian rhythm and the time of the sleep wake cycle based on geographic location. This often occurs as people travel across time zones.

Circadian rhythm sleep disorder, shift work type – Many individuals who work shift work experience insomnia or excessive sleepiness which vary depending on their scheduled work hours.

Circadian rhythm sleep disorder due to medical condition – Individuals with this disorder have a medical or neurological condition which accounts for the circadian rhythm disturbance.

Other circadian rhythm sleep disorder – These are circadian rhythm disorders which do not meet the criteria for a specific disorder.

Other circadian rhythm sleep disorder due to drug or substance – These individuals demonstrate a circadian rhythm sleep disorder which is directly related to the use or abuse of a substance or drug.

Other circadian sleep disorder due to alcohol use – These individuals demonstrate a circadian rhythm sleep disorder which is directly related to the use or abuse of alcohol.