A seizure is a sudden, uncontrolled electrical disturbance in the brain. It can cause changes in your behavior, movements or feelings, and in levels of consciousness. If you have two or more seizures or a tendency to have recurrent seizures, you have epilepsy. There are many types of seizures, which range in severity. Seizures are changes in your brain's electrical activity. This change can cause dramatic, noticeable symptoms or even no symptoms. Seizures usually come on suddenly. How long and severe they are can vary. A seizure can happen to you just once, or over and over. A sudden surge of electrical activity in the brain, a seizure usually affects how a person feels or acts. About 1 out of 10 people may have a seizure during his or her lifetime. Do I call 911? Seizures do not usually require emergency medical attention.