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 (cf. 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. Somnolence goes back to the Latin "somnus" meaning "sleep."



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
  4. ^ The World Professional Association for Transgender Health's Standards of Care, 6th version

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Look at other dictionaries:

  • somnolence — [ sɔmnɔlɑ̃s ] n. f. • v. 1380, rare av. XIXe, sens 2; bas lat. somnolentia 1 ♦ (1530) État intermédiaire entre la veille et le sommeil, perte de conscience et engourdissement momentanés. ⇒ demi sommeil, torpeur. Médicament qui peut amener un état …   Encyclopédie Universelle

  • Somnolence — Som no*lence, Somnolency Som no*len*cy, n. [L. somnolentia: cf. F. somnolence.] Sleepiness; drowsiness; inclination to sleep. [1913 Webster] …   The Collaborative International Dictionary of English

  • somnolence — index languor Burton s Legal Thesaurus. William C. Burton. 2006 …   Law dictionary

  • somnolence — late 14c., from O.Fr. sompnolence, from L. somnolentia sleepiness, from somnolentus, from somnus sleep, from PIE *swep no, from root *swep sleep (Cf. Skt. svapnah, Avestan kvafna , Gk. hypnos, Lith. sapnas, O.C.S. sunu, O …   Etymology dictionary

  • Somnolence — Sommeil Pour les articles homonymes, voir Sommeil (homonymie). Chaton endormi …   Wikipédia en Français

  • Somnolence — Sleepiness, the state of feeling drowsy, ready to fall asleep. A person experiencing somnolence is somnolent and is acting somnolently. Somnolence, somnolent, and somnolently go back to the Latin somnus meaning (please don t yawn) sleep. * * *… …   Medical dictionary

  • somnolence — (so mno lan s ) s. f. Terme de médecine. Assoupissement peu profond, mais pénible et insurmontable.    Fig. Engourdissement moral. ÉTYMOLOGIE    Provenç. sompnolencia ; espagn. somnolencia ; ital. sonnolenza ; du lat. somnolentia, de somnolentus …   Dictionnaire de la Langue Française d'Émile Littré

  • SOMNOLENCE — s. f. (On prononce l M.) T. de Médec. État intermédiaire entre le sommeil et la veille ; Disposition habituelle à dormir. État de somnolence …   Dictionnaire de l'Academie Francaise, 7eme edition (1835)

  • SOMNOLENCE — n. f. état intermédiaire entre le sommeil et la veille. état de somnolence …   Dictionnaire de l'Academie Francaise, 8eme edition (1935)

  • somnolence — somnolent ► ADJECTIVE 1) sleepy; drowsy. 2) inducing drowsiness. DERIVATIVES somnolence noun somnolently adverb. ORIGIN Latin somnolentus, from somnus sleep …   English terms dictionary

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