ABSTRACT
Sleepiness, like hunger or thirst, is a common experience difficult to define and measure. Sleepiness appears normally during the process of falling asleep as an indicator to the organism that sleep is approaching; it can be prolonged by resisting sleep and disappears after getting enough sleep. These are normal phenomena. Sleepiness, however, becomes abnormal when it is “excessive,” that is, when because of its frequency or intensity, it appears under abnormal circumstances and interferes with daytime activities (1). Excessive daytime sleepiness (EDS) may happen despite devoting enough time to sleep. One can realize by reading the above statements that they generate more questions than answers: What does excessive really mean? What is an “abnormal circumstance”? How much sleep is “enough”? What type of daytime activity are we referring to? These questions and the fact that EDS in general develops insidiously explain why patients with EDS take so long to look for medical help, in contrast with other neurological symptoms such as a seizure or a limb palsy.
