Sleep inertia is a physiological state characterised by a decline in motor dexterity and a subjective feeling of grogginess immediately following an abrupt awakening. The 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 may take several hours to dissipate. In the majority of cases, morning sleep inertia is experienced for 15 to 30 minutes after waking.
- Depth of sleep when awakened. After roughly 10–30 minutes, the brain enters into slow-wave sleep. Being awakened during this stage yields more sleep inertia than awakening from other stages of sleep.
- 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 had a strong circadian rhythm. "Sleep inertia is the impaired cognitive performance immediately upon awakening, which decays over tens of minutes. This phenomenon has relevance 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 the last 66 hours of an 88-hour period of wakefulness that included seven two-hour naps. Lapses in attention were examined after awakening from 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 is directly related to sleep stage at awakening; persons awakened during the deepest sleep have the slowest reaction times.
Testing of mental arithmetic capability after one- and two hour 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.
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. Sleep inertia may also be the result of lower levels of glucose being available than during wakefulness - The gradual dissipation of sleep inertia could be attributed to the effects of Glucagon on Glycogen shortly after awakening, and the gradual increase in blood glucose to a normal level, assisted and achieved by eating as well.
- Tassi, P.; Muzet, A. (2000). "Sleep inertia". Sleep Medicine Reviews 4 (4): 341–353. doi:10.1053/smrv.2000.0098. PMID 12531174.
- Wertz, A.T.; Ronda, J.M.; Czeisler, C.A.; Wright Jr, K.P. (2006). "Effects of Sleep Inertia on Cognition". JAMA: the Journal of the American Medical Association 295 (2): 163–4. doi:10.1001/jama.295.2.163. PMID 16403927.
- Jewett, ME; Wyatt, JK; Ritz-De Cecco, A; Khalsa, SB; Dijk, DJ; Czeisler, CA (1999). "Time course of sleep inertia dissipation in human performance and alertness". Journal of Sleep Research 8 (1): 1–8. doi:10.1111/j.1365-2869.1999.00128.x.
- "What Is Sleep Inertia? - Sleeping Expert". Sleeping Expert. Retrieved 2015-11-09.
- "Alertness management: strategic naps in operational settings" (PDF).
- "Overview, Waking, Non-REM, REM, Sleep Cycle, Factors, Age".
- Wilkinson, RT; Stretton, M (1970). "Performance After Awakening at Different Times of Night".
- Scheer, FAJL; Shea, TJ; Hilton, MF; Shea, SA (2008). "An endogenous circadian rhythm in sleep inertia results in greatest cognitive impairment upon awakening during the biological night". Journal of Biological Rhythms 23 (4): 353–361. doi:10.1177/0748730408318081.
- Van Dongen, HP; Price, NJ; Mullington, JM; Szuba, MP; Kapoor, SC; Dinges, DF (2001). "Caffeine eliminates psychomotor vigilance deficits from sleep inertia" (PDF). Sleep 24 (7): 813–819. PMID 11683484.
- Sherry, Patrick (June 2000). "Fatigue Countermeasures in the Railroad Industry: Past and Current Developments" (PDF). University of Denver. Retrieved 2009-05-11.
- Dinges, DF (1990). Bootzin, RR; Kihlstrom, JF; Schacter, DL, eds. Are you awake? Cognitive performance and reverie during the hypnopompic state. American Psychological Association. pp. 159–175. ISBN 1-55798-083-7.