Somnolence (or "sleepiness") 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" is derived from the Latin "somnus" meaning "sleep."
The human body can become sleepy in response to infection. Such somnolence is one of several sickness behaviors or reactions to infection that some theorize evolved due to promoting recovery by conserving energy while the body fights the infection using fever and other means.
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