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Generalized tonic-clonic seizures are bilateral and symmetric generalized motor seizures, that occur in an individual with loss of consciousness. The tonic-clonic seizure consists of a tonic (bilateral increased tone, lasting seconds to minutes) and then a clonic (bilateral sustained rhythmic jerking) phase, typically in this order, however variations such as clonic-tonic-clonic and myoclonic-tonic-clonic can also occur.

A clonic seizures is a seizure with bilateral, sustained rhythmic jerking and loss of consciousness. It is distinguished from repetitive serial myoclonic seizures by the rhythmicity of the jerking and that it occurs in the setting of loss of consciousness. Repetitive serial myoclonic seizures (for example in myoclonic status epilepticus) are associated with irregular jerking, often with partially retained awareness.

CAUTION Although asymmetry, such as head and eye deviation, can occur in a generalized onset motor seizure, if consistent focal features are seen from seizure to seizure right arrow consider a focal to bilateral tonic-clonic seizure or a focal bilateral motor seizure.

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