Somnolence (or "drowsiness") is a state of near-sleep, a strong desire for sleep, or sleeping for unusually long periods. 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. Somnolence goes back to the Latin "somnus" meaning "sleep."