Grand mal: A form of epilepsy characterized by tonic-clonic seizures. involving two phases -- the tonic phase in which the body becomes rigid, and clonic phase in which there is uncontrolled jerking. Tonic-clonic seizures may or may not be preceded by an aura, and are often followed by headache, confusion, and sleep. They may last for mere seconds, or continue for several minutes. If a tonic-clonic seizure does not resolve or if such seizures follow each other in rapid succession, seek emergency help. The person could be in a life-threatening state known as status epilepticus. Treatment is with antiseizure medications.