Driver sleepiness and sleep disorders, with particular reference to Parkinson's disease

Falling asleep while driving accounts for a significant proportion of vehicle accidents under monotonous driving conditions. Time of day (circadian) effects are profound, and are as important in determining driver sleepiness as is the duration of a drive. Older drivers are particularly Vulnerable to sleepiness in the mid-afternoon. Only a minority of these accidents seem to be due to pathological causes of sleepiness. Patients liable to increased daytime sleepiness must be told that driving in this state is dangerous and that they have a duty of care toward other road users. Parkinson's disease (PD) often causes a variety of night-time sleep disturbances and excessive daytime sleepiness, although the association between the two may be complex. There is little evidence to show that PD can result in sudden, unforewarned 'sleep attacks' In healthy people, sleep does not occur spontaneously without warning. Although healthy drivers falling asleep are unlikely to recollect having done so (also claiming 'sleep attacks'), they would have been aware of the precursory state of increasing sleepiness; probably reaching a state of fighting off sleep prior to an accident. Putative countermeasures to sleepiness, adopted during continued driving (e.g. cold air, use of car radio) are only effective for a short while, even in healthy, sleepy individuals. The only safe countermeasure to driver sleepiness, particularly when the driver reaches the stage of fighting sleep, is to cease driving - and, perhaps, take a 30-min break encompassing a short nap (<15 min) and/or coffee (about 150 mg caffeine).