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 ^[1], and the chronic condition referring to being in that state independent of a circadian rhythm. Somnolence goes back to the Latin "somnus" meaning "sleep." It is also stongly assciated with mental fatigue or lethargy.