Shifted sleep hours.

This paper reviews the effects of suboptimal timing of the sleep/wake cycle on sleep, alertness and well-being. It is seen that shift work and rapid travel across time zones causes disturbed sleep and increased fatigue. These effects are mainly due to sleep being displaced to a rising phase of the circadian rhythm at which the interference with sleep is at its maximum. The process may also be reversed such that pathological changes of the circadian rhythm may require sleep patterns incompatible with those of the rest of society. The review concludes with a discussion of possible counter measures.