ABSTRACT
Somnolence is a complex state, impacted by multiple determinants such as quantity and quality of prior sleep, circadian time, drugs, attention, motivation, environmental stimuli, and various medical, neurological, and psychiatric conditions. Clearly, somnolence is welcomed when sleep is desired, but at other times often becomes an unwanted symptom. Pathological or inappropriate somnolence is clinically termed hypersomnia or excessive daytime sleepiness (EDS). Subjects with hypersomnia are unable to stay alert and awake during the major waking episodes of the day, resulting in unintended lapses into sleep.
