Sleep inertia

Sleep inertia is a physiological state characterized by a decline in motor dexterity and a subjective feeling of grogginess immediately following an abrupt awakening. This impaired alertness may interfere with the ability to perform mental or physical tasks. Sleep inertia can also refer to the tendency of a person wanting to return to sleep.

Sleep inertia occurs normally after awakening. Upon awakening in the morning, subjective alertness and mental performance are significantly impaired. Morning sleep inertia takes two to four hours to dissipate completely, though individuals may function adequately before that time.

Factors

A variety of factors influence the severity and duration of sleep inertia:

• Depth of sleep when awakened: Awakening during the slow-wave sleep stage yields more sleep inertia than awakening from other stages of sleep. However, since one cannot predict accurately the stages of sleep that will occur within a nap, there is no physiological reason to try to limit the length of a nap. When one is sleep deprived, any sleep is beneficial.
• Timing of sleep: Sleep inertia is thought to be related to the phase of the body's circadian rhythm. Sleep inertia in terms of a serial addition task has a strong circadian rhythm. This phenomenon is relevant to people who need to make important decisions soon after awakening, such as on-call emergency workers.
• Chemical influences: Drugs such as caffeine can suppress the effect of sleep inertia, possibly by blocking adenosine receptors in the brain. Sustained low-dose caffeine was examined as a sleep inertia countermeasure during extended periods of wakefulness that included short naps. Performance was impaired significantly in the placebo condition but not with caffeine, and caffeine had only modest effects on nap sleep structure.
• Reaction time performance: Reaction time performance is directly related to sleep stage at awakening; individuals awakened during the deepest sleep have the slowest reaction times.

Testing of mental arithmetic capability after short naps at all times of day and night and after varying amounts of sleep and sleep deprivation demonstrated an inertia characterized by social interaction but with simultaneous performance impairment, reverie, and misjudgment of sleepiness.

Cause

One theory is that sleep inertia is caused by the build-up of adenosine in the brain during NREM sleep. Adenosine then binds to receptors, and feelings of tiredness result.

See also

• Circadian rhythm
• Sleep deprivation
• NREM sleep
• Caffeine
• Delayed sleep phase syndrome
• Shift work

External links

• Flying Safely Article on Napping