The most severe of all convulsive seizures is the:

The most severe form of convulsive seizures is the tonic-clonic seizure, also known as a grand mal seizure. This type of seizure includes both tonic (stiffening of muscles) and clonic (rhythmic jerking) phases, which can result in a loss of consciousness and may last for several minutes. During these seizures, a person experiences intense muscle contractions followed by rapid muscle contractions, which can lead to falls and potential injury.

The severity of tonic-clonic seizures is further evidenced by their potential for longer duration compared to other seizure types and the recovery period often required afterward, which can include fatigue, confusion, or disorientation. In contrast, simple and complex partial seizures typically do not involve the same degree of convulsive activity or loss of consciousness, while absence seizures tend to present as brief episodes of staring and do not involve the convulsive movements characteristic of tonic-clonic seizures. Thus, the tonic-clonic seizure stands out as the most severe form due to its dramatic physical manifestations and impact on the individual's overall health.