Definition of Tonic Seizure

Tonic seizure is a seizure characterized by a sudden onset of tension or stiffness in the muscles of the body, arms, or legs. Tonic seizures are most common during sleep and usually last about 20 seconds or less. If a person is standing when a tonic seizure occurs, they may fall. The seizure may start in one part of the brain or in different parts of the brain at the same time. The individual may only have a small change in awareness during this type of seizure.