Tonic seizures are fairly uncommon. They occur mostly in people with Lennox-Gastaut syndrome. This is a severe form of generalized epilepsy that begins in early childhood. (Children with Lennox-Gastaut syndrome may also have atonic seizures.)
When a tonic seizure occurs, the muscles in the body contract and the entire body stiffens. This occurs suddenly and without warning. And it often causes the person to fall down.
People who have tonic or atonic seizures are likely to be injured when they fall. Children may have to wear helmets and restrict their activities to prevent serious injury.