Sleep is known to facilitate epileptic manifestations but can also protect the sleeper against the recurrence of seizures. This has been demonstrated in studies on sleep deprivation, and is particularly evident in alcoholic epilepsy and matutinal myoclonus epilepsy. Sleep organization in the epileptic patient is permanently altered by frequent awakenings and stage shifts. Nocturnal grand mal and repetitive partial seizures worsen the sleep disorder by reducing total sleep time and decreasing REM percentage by half. The cumulative effect of these sleep disorders may act on day-time vigilance in epileptics, and may even exert an influence on the recurrence of seizures.