Somnolence (alternatively "
sleepiness" or "
drowsiness") is a state of strong desire for
sleep, or sleeping for unusually long periods (compare
hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep, the condition of being in a drowsy state due to
circadian rhythm disorders, or a symptom of other health problems. It can be accompanied by
lethargy, weakness, and lack of mental agility.