Nocturnal seizures are usually tonic-clonic. They might occur just after a person has fallen asleep, just before waking, during daytime sleep, or while in a state of drowsiness. People who experience nocturnal seizures may find it difficult to wake up or to stay awake. Although unaware of having had a seizure while asleep, they may arise with a headache. They may have temper tantrums or other destructive behaviour throughout the day.

Nocturnal seizures are very uncommon and their mechanisms poorly understood. The majority of people with nocturnal seizures have idiopathic epilepsy. There is evidence that sleep enhances epileptic discharges in the EEG, though their daytime recordings may appear to be normal. If a pattern of limiting seizures to the hours of slumber is maintained, the chance of them occurring during the daytime is greatly reduced.

Phenytoin may be used to control, or perhaps prevent, nocturnal seizures.