Sleep Inertia | Causes of Sleep Inertia

Sleep Inertia

Sleep inertia or grogginess is a transitional state of lowered arousal occurring immediately after awakening from sleep.

Sleep inertia can last from 1-5 minutes in non-sleep deprived subjects but typically lasts longer if the nap follows a prolonged period of wakefulness. During this period, the capacity level is reduced and may have trouble doing even simple everyday actions.

Effects of sleep inertia:

  1. Decrease in memory ability.
  2. Impairment of the capability to make decisions.
  3. Impairment of performance and response time on tasks.

Sleep inertia is a normal part of life most of the time and is nothing to worry about. There are a couple times when it is important, however:

  1. If someone is sleep deprived or has been woken from a deep sleep stage, the sleep inertia can be more severe than normal and may take longer to overcome. People should try to be alert of their sleep inertia and compensate in their activities for it.
  2. A lot of drowsy driving accidents occur early in the morning, not when the driver has been up too long, but when he or she has recently awoken and is still suffering from sleep inertia. Sleep inertia in a driver behind the wheel can be very risky as the impairment of motor and cognitive functions can affect a person's ability to drive safely.

Causes for sleep inertia:

  1. Sudden awakening of sleep, the effects are  supposed to last up to 30 minutes or more
  2. Sleep deprivation, which will increase the cause of sleep inertia.
  3.  It will cause less impairment as the time between awakening and task performance increases.
  4.  If you are woken from deep or slow wave sleep, the effects of it are more noticeable. Slow wave sleep is more likely to occur during the early stages of sleep.
  5.  In a well rested person, slow wave sleep generally occurs within 45-60 minutes.
  6. Performance accuracy is more impaired by sleep inertia than reaction time.
  7. Sleep inertia is more extreme when awakening occurs near the trough of the core body temperature as compared to its circadian peak.
  8. Many people experience sleep inertia even after short naps.

Finally, sleep disorders represent risk factors which deserve new insight in treatment strategies to counteract the adverse effects of sleep inertia.


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