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Somnolence: Wikis


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Classification and external resources
ICD-10 R40.0
ICD-9 780.09

Somnolence (or "drowsiness") is a state of near-sleep, a strong desire for sleep, or sleeping for unusually long periods (c.f. hypersomnia). It has two distinct meanings, referring both to the usual state preceding falling asleep, and the chronic condition referring to being in that state independent of a circadian rhythm. The disorder characterized by the latter condition is most commonly associated with the use of prescription medications such as mirtazapine or zolpidem.

It is considered a lesser impairment of consciousness than stupor or coma.



Sleepiness can be dangerous when performing tasks that require constant concentration, such as driving a vehicle. When a person is sufficiently fatigued, he or she may experience microsleeps.


The human body can become sleepy in response to infection.[1] Such somnolence is one of several sickness behaviors or reactions to infection that some theorize evolved to promote recovery by conserving energy while the body fights the infection using fever and other means.[2][3]

Associated conditions

See also


  1. ^ Mullington, J., Korth, C., Hermann, D. M., Orth, A., Galanos, C., Holsboer, F. Pollmacher, T. (2000) "Dose-dependent effects of endotoxin on human sleep". Am J Physiol Regul Integr Comp Physiol. 278: R947-955 PubMed
  2. ^ Hart, B. L. (1988) "Biological basis of the behavior of sick animals". Neurosci Biobehav Rev. 12: 123-137. PubMed
  3. ^ Kelley, K. W., Bluthe, R. M., Dantzer, R., Zhou, J. H., Shen, W. H., Johnson, R. W. Broussard, S. R. (2003) "Cytokine-induced sickness behavior". Brain Behav Immun. 17 Suppl 1: S112-118 PubMed

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