A seizure occurs when there’s abnormal electrical activity in the brain. Seizures may go virtually unnoticed. Or, in severe cases, they may produce a change or loss of consciousness and involuntary muscle spasms called convulsions. Seizures usually come on suddenly and vary in duration and severity. A seizure may be a one-time event, or you may have seizures repeatedly. Recurrent seizures are called epilepsy, or a seizure disorder. Less than one in 10 people who has a seizure develops epilepsy.
Experts classify seizures into two general categories and many subtypes based on the pattern of the attack.
Epilepsy is a general term for the tendency to have seizures. Epilepsy is usually diagnosed only after a person has had more than one seizure.
When identifiable, the causes of epilepsy usually involve some form of injury to the brain. For most people, though, epilepsy's causes aren't known.
Generalized seizures involve both sides of the brain from the start of the attack. Common subtypes include tonic-clonic (grand mal) and absence seizures (petit mal). Febrile and infantile spasms are two types of generalized seizures that occur almost exclusively in young children.
Partial (or focal) seizures are the second major seizure type. These begin in a specific area of the brain and may be contained there. Or they may spread to the entire brain.
With simple partial seizures, the person remains conscious.