A seizure that involves a loss of consciousness and violent muscle contractions.

A tonic-clonic seizure causes a loss of consciousness and violent muscle contractions. It's usually caused by epilepsy. But it may have other triggers such as very low blood sugar, high fever or a stroke.

During the seizure, the person loses consciousness, the muscles contract suddenly and the person falls. Then the muscles alternately flex and relax for 1 to 2 minutes.

Many people have only one seizure and don't need treatment. Others may need daily medicines to control and prevent seizures. If medicines aren't effective, surgery or another treatment may be an option. Emergency care is needed if the seizure lasts more than five minutes.