Sleep inertia

Sleep inertia is a physiological state characterised by a decline in motor dexterity and a subjective feeling of grogginess, immediately following an abrupt awakening from deep sleep. Sleep inertia can also refer to the tendency of a person to want to return to sleeping, even after suitable rest has been achieved. Typically, sleep inertia lasts between 1 to 3 hours for a night wake up and 45 to 90 minutes for a day wake up. If the subject is awakened due to a perceived danger, however, the duration of sleep inertia is reduced to only a few seconds.

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Factors

NASA studies have shown that a variety of factors influence the severity and duration of sleep inertia. These include:

• Depth of sleep when woken. After roughly 30 minutes, the body enters into deep sleep. Waking from deep sleep induces more sleep inertia than otherwise.

• Time of sleep. Sleep inertia is thought to be related to the phase of the body's circadian rhythm. Waking during a trough in body temperature tends to produce more sleep inertia.

• Chemical influences. Studies have shown that drugs such as caffeine suppress the effect of sleep inertia, possibly by blocking adenosine receptors in the brain.

Cause

The cause of sleep inertia is not clear. One theory is that it is caused by the build-up of adenosine in the brain during non-REM sleep. Adenosine then binds to receptors, which produce the feelings of tiredness.

See also

• Circadian rhythm sleep disorder
• Delayed sleep phase syndrome