[Fatigue, drowsiness and sleep].

Vigilance is a critical output of adaptative processes related to sleep/wake continuity and circadian rhythms. Since vigilance is highly stressed in the modern technic society, its sudden failures, expressed as fatigue, drowsiness and/or sleepiness, may be dramatically involved in accident's incidence, as observed in work accidents, manufacturing and transport sectors and private life. There is a detectable human factor involved in 70% of cases. Even if there are multifactorial circumstances, human factor such as fatigue, overwork or errors in decision are generally reported. Two main cases may be described: on one hand sleepiness and fatigue occur as sleep deprivation builds up, with an excessive duration of wakefulness (that suggests that it may be prevented by information and hygienic precautions), on the other hand sleepiness is the expression of a sleep illness or disease (and it must be detected early by a clinical biological survey). Three levels are reviewed and discussed for a comprehensive view of abnormal fatigue and sleepiness: what is the prevalence as evaluated by epidemiologic, biologic and psychologic methods? is there any specificity of cognitive disturbances associated with intrinsic or rhythmic dyssomnic illness and how can one evaluate or measures them? on the basis of some experimental reports in normal subjects by changing wake and sleep schedules it is assumed that the recovery which follows a sleep deprivation may be quite different when there is an early or a late night sleep deprivation. Possibilities for self-sleep training are discussed. The actual great interest in abnormal sleepiness is supported by its human and socio-economic consequences. If new pharmacological or physiological treatments have recently be suggested, information and cooperation are required in healthy subjects and in patients. Self-detection in the course of sleepiness is a critical factor: it may be learned and taught by medical preventive projects.