Work hours and sleepiness.

The present paper finds that shift work is associated with severe sleepiness on the night shift and to some extent on the morning shift. This sleepiness is at least as severe as that seen in hypersomnia and is associated with a strongly increased risk of accidents. The reason for night shift sleepiness is work at the circadian nadir, extended periods of wakefulness, and truncated sleep. Much of the sleepiness in shift work may be predicted using a quantitative model.