Generalized tonic–clonic seizure

A generalized tonic–clonic seizure, commonly known as a grand mal seizure or GTCS, is a type of generalized seizure that produces bilateral, convulsive tonic and clonic muscle contractions. Tonic–clonic seizures are the seizure type most commonly associated with epilepsy and seizures in general and the most common seizure associated with metabolic imbalances. It is a misconception that they are the sole type of seizure, as they are the main seizure type in approximately 10% of those with epilepsy.

These seizures typically initiate abruptly with either a focal or generalized onset. A prodrome (a vague sense of impending seizure) may also be present before the seizure begins. The seizure itself includes both tonic and clonic contractions, with tonic contractions usually preceding clonic contractions. After these series of contractions, there is an extended postictal state where the person is unresponsive and commonly sleeping with loud snoring. There is usually pronounced confusion upon awakening.