This article is from the Epilepsy FAQ, by Andrew Patrick (email@example.com) with numerous contributions by others.
The tonic-clonic (formerly grand mal) seizure is a generalized
convulsion involving two phases. In the tonic phase, the individual
loses consciousness and falls, and the body becomes rigid. In the
clonic period, the body extremities jerk and twitch. After the seizure,
consciousness is regained slowly. If the tonic-clonic seizure begins
locally (with a partial seizure) it may be preceded by an "aura". These
seizures are said to be secondarily generalized.
While the tonic-clonic seizure is the most visible, obvious type of
Epilepsy, it is not the most common. Partial seizures are more
frequently encountered and occur in 62% of all Epilepsy patients.
Complex-partial seizures account for approximately 30% all cases.