Sleep inversion

Sleep inversion or sleep-wake inversion is a reversal of sleeping tendencies. Individuals experiencing sleep-wake inversion exchange diurnal habits for nocturnal habits, meaning they are active at night and sleep during the day. Sleep-wake inversion, when involuntary, can be a sign of a serious disorder.

Circadian rhythm sleep disorder involves an alteration of an individual's circadian system or a mismatch between a person's natural, or endogenous, circadian system and the external, or exogenous, demands placed on it. It can lead to insomnia at certain times of the day or excessive sleepiness throughout the day. The insomnia or excessive sleepiness results in impaired functioning in social, occupational, or other environments.

The delayed sleep phase type of circadian rhythm sleep disorder is marked by a delay of the sleep-wake cycle as it relates to the demands of society. It is often due to a psychosocial stressor (an event in a person's environment that causes stress or discomfort), especially for adolescents. The delayed sleep-wake cycle leads to chronic sleep deprivation and habitually late sleeping hours. Individuals with this type often have difficulty changing their sleeping patterns to an earlier and more socially acceptable time. Their actual sleep, once it begins, is normal. It is the timing of their sleeping and waking that is persistently delayed.

The jet lag type of circadian rhythm sleep disorder is characterized by disruptions arising from a mismatch between a person's circadian cycle and the cycle required by a different time zone. The more time zones that are traveled, the greater the disruption. Eastbound travel, in which sleep-wake hours are advanced, typically causes more problems than westbound travel, in which sleep-wake hours are delayed. People who travel often and cross many time zones when they travel are most susceptible to this type.

The shift work type of circadian rhythm sleep disorder is distinguished by disruptions due to a conflict between a person's endogenous circadian cycle and the cycle required by shift work. Individuals who work the night shift often experience this problem, especially those people who switch to a normal sleep schedule on days off. Also, people who work rotating shifts experience this problem because of the changing sleep-wake schedules they experience. The disruptions caused by shift work result in inconsistent circadian schedules and an inability to adjust to the changes consistently.

The unspecified type of circadian rhythm sleep disorder is characterized by a pattern of sleep-wake disturbance and circadian mismatch that is not due to the causes of the other three types. Examples of other causes include irregular sleep-wake patterns and non-24-hour sleep-wake patterns. If an individual's sleep-wake pattern is based on a period of time of slightly more than 24 hours, their circadian rhythm can become progressively delayed.

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