A seizure, technically known as an epileptic seizure, is a brief episode of signs or symptoms due to abnormally excessive or synchronous neuronal activity in the brain. The outward effect can vary from uncontrolled jerking movement (tonic-clonic seizure) to as subtle as a momentary loss of awareness (absence seizure). Diseases of the brain characterized by an enduring predisposition to generate epileptic seizures are collectively called epilepsy.
Seizures can also occur in people who do not have epilepsy for various reasons including brain trauma, drug use, elevated body temperature, low blood sugar and low levels of oxygen. Additionally, there are a number of conditions that look like epileptic seizures but are not.
A seizure is a medical emergency. A first seizure generally does not require long term treatment with anti-seizure medications unless there is a specific problem on either electroencephalogram or brain imaging.
5–10% of people who live to 80 years old have at least one epileptic seizure and the chance of experiencing a second seizure is between 40% and 50%. About 50% of patients with an unprovoked apparent "first seizure" have had other minor seizures, so their diagnosis is epilepsy. Epilepsy affects about 1% of the population currently and affected about 4% of the population at some point in time. Most of those affected—nearly 80%—live in developing countries.