Clinical approach to excessive daytime sleepiness

Subjective sleepiness is defined as "an elemental feeling state" by which t he subject, and only him/her knows whether he/she is alert or sleepy. Subje ctive sleepiness has little been used for the clinical evaluation of sleepi ness. Objective sleepiness is defined as a consequence of the homeostatic need fo r sleep. In the absence of a measurable marker of the fulfillment of the fu nction of sleep, the evaluation of objective sleepiness has to rely on a be havioral approach based on the postulate that the more you need sleep (i.e. , the sleepier you are), the more likely you are to fall asleep. However, a s for many other fundamental human behaviors (drinking, eating, sexual beha vior), it is likely that the sleeping behavior serves other purposes than i ts primary objective, which distorts the relationship between the observed sleeping behavior and the actual need for sleep. The likelihood to fall asl eep can be measured by the speed with which a sleep episode occurs under st andardized laboratory conditions (multiple sleep latency test, maintenance of wakefulness test, OSLER test), or by the frequency of unwanted sleep epi sodes under the more naturalistic conditions of daily life (Epworth Sleepin ess Scale). These various approaches have advantages and drawbacks, but non e of them can be considered the "gold standard".