The brain controls how the body moves by sending out small electrical signals through the nerves to the muscles. Seizures, or convulsions, occur when abnormal signals from the brain change the way the body functions.

Seizures are different from person to person. Some people have only slight shaking of a hand and do not lose consciousness. Other people may become unconscious and have violent shaking of the entire body.

Shaking of the body, either mild or violent, does not always occur with seizures. Some people who have seizures have symptoms before the seizure (auras) or briefly lose touch with their surroundings and appear to stare into space. Although the person is awake, he or she does not respond normally. Afterwards, the person does not remember the episode.

Not all body shaking is caused by seizures. Many medical conditions can cause a type of body shaking that usually affects the hands and head (tremors).

A small number of people will have only one seizure during their lifetime. A single seizure usually lasts less than 3 minutes and is not followed by a second seizure. Any normally healthy person can have a single seizure under certain conditions. For instance, a sharp blow to the head may cause a seizure. Having one seizure does not always mean that a serious health problem exists. But if you have a first-time seizure, you should be checked by your doctor. It is important to rule out a serious illness that may have caused the seizure. Fever seizures (febrile convulsions) are the most common cause of a single seizure, especially in children. For more information, see the topic Fever Seizures.

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