A generalized seizure is a sudden change in consciousness, muscle control or behavior caused by abnormal activity on both sides of the brain. A generalized seizure is different from a partial (focal) seizure, which usually affects a small, localized area of the brain.

Seizures occur when the neurons in the brain suddenly increase activity, causing an electrical storm that can overwhelm the brain. This can result in various symptoms depending on the area of the brain affected. People who have a generalized seizure usually experience symptoms that affect their entire body, such as whole-body muscle contractions or a loss of consciousness.

The most identifiable and traumatic type of generalized seizure is the tonic-clonic seizure, also known as grand mal seizures or convulsions. Many tonic-clonic seizures are isolated events and, although distressing to witness, rarely cause neurological damage.

Generalized seizures may be caused by chronic underlying medical conditions that may require treatment (e.g., epilepsy). Many generalized seizures have no known cause, making them difficult to prevent. In cases where the underlying cause is unknown, seizures can sometimes be controlled with medication.

Generalized seizures can rarely be treated with brain surgery because the abnormal neuron activity occurs in the entire brain. However, people with recurrent generalized seizures that are poorly controlled by medication may be suitable for a type of treatment called vagus nerve stimulation.

There are certain things bystanders can do (and not do) to prevent additional harm to a person having a generalized seizure. For example, nothing should be placed in a person’s mouth during a seizure, and restraint should not be used. It is recommended that bystanders clear the area of furniture and objects that may cause injury to the person having a seizure. Also, the person having the seizure should be gently rolled onto his or her side to prevent choking on vomit or mucus.