Print. Epilepsy is a central nervous system disorder (neurological disorder) in which nerve cell activity in the brain becomes disrupted, causing seizures or periods of unusual behavior, sensations and sometimes loss of consciousness.Seizure symptoms can vary widely.bout 1 in 26 people in the United States will develop a seizure disorder. Nearly 10 percent of individuals may have a single unprovoked seizure. However, a single seizure doesn't mean you have epilepsy. At least two unprovoked seizures are generally required for an epilepsy diagnosis.