Sleepiness

Sleepiness may be defined as an individual’s perceived need and/or readiness for sleep, and in hypersomnia disorders, sleepiness is usually experienced as an inappropriate, unpleasant, and excessive feeling. This article explores different clinical types of sleepiness including paroxysmal, inertial, labile, recurrent, or silent sleepiness, as well as the contexts in which these manifestations occur, then turns attention toward interindividual differences or ‘trototypes’ in vulnerabilities to sleepiness, and the potential biological underpinnings of such differences which may involve circadian and adenosinergic regulatory genes and other genetic mechanisms controlling sleep homeostasis. Exogenous environmental and endogenous gender and aging influences on sleepiness are also considered.