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. Typically, sleep inertia lasts between 1 and 30 minutes though if the person was awakened due to a danger it is reduced to only a few seconds.

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


 * Length of sleep. 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.