Seizures are sudden bursts of abnormal electrical activity in the brain that may affect a person's muscle control, movement, speech, vision, or awareness (consciousness). The effects of seizures depend on a person's individual response, as well as the seizure type, frequency, and severity.

Some seizures make a person fall to the ground in convulsions, in which the muscles stiffen or jerk out of control. Others may stare as if in a trance, have only a few muscle twitches, or sense a strange smell or visual disturbance not experienced by anyone else.

Sometimes a seizure is a symptom of another medical problem, such as a high fever (especially in children), a stroke, infection, low blood sugar (hypoglycemia), very low blood pressure, or a brain tumour.