What Are Seizures? What Causes Them?

A seizure happens because of abnormal electrical activity in the brain. It may go nearly unnoticed. Or, in some severe cases, it may cause unconsciousness and convulsions, when your body shakes uncontrollably.

Seizures usually come on suddenly. How long and severe they are can vary. A seizure can happen to you just once, or over and over. If they keep coming back, that's epilepsy, or a seizure disorder. Less than one in 10 people who have a seizure get epilepsy.

Experts put seizures into two general categories:

Generalized Seizures

These involve your entire brain from the start. Common subtypes include:

Tonic-clonic (grand mal): This is the most common subtype. Your arms and legs get stiff, and you may stop breathing for a bit. Then your limbs will jerk around. Your head will move about, as well.

Absence seizures (petit mal): You lose awareness briefly when you have one of these. Children get them more often than adults. Typically, they last only a few seconds.

Febrile seizures: These are convulsions a child may have from a high fever caused by an infection. They can last a few minutes but are usually harmless.

Infantile spasms: These usually stop by age 4. The child's body gets stiff suddenly and his head goes forward. Many kids who have these get epilepsy later in life.

Partial (Focal) Seizures

This type begins in a specific area of the brain. They may spread to the entire brain. There are two types:

If you have a focal onset aware seizure, you remain conscious. The seizure is very brief (usually less than 2 minutes). You may or may not be able to respond to people while it's happening.

Focal onset impaired awareness seizures can cause unconsciousness. You may also do things without knowing it, like lip smacking, chewing, moving your legs, or thrusting your pelvis.

What Causes Seizures?

Often, it's unknown. Many things can bring them on, including:

WebMD Medical Reference Reviewed by Neil Lava, MD on March 6, 2019



American Academy of Neurology. 

Bazil, C. Living Well with Epilepsy and Other Seizure Disorders: An Expert explains What You Really Need to Know. Collins, 2002. 

Strafstrom, C. Epilepsy Curriculum, November 2004. 

Nadkarni, S. Neurology, June 2005. 

Bialer M. Epilepsy Research, September/October 2004.

Mayo Clinic: "Febrile seizure."

Epilepsy Foundation: "Focal Onset Aware Seizures (simple partial seizures), "Generalized Seizures," "Focal Onset Impaired Awareness Seizures (complex partial seizures)," "Infantile Spasms/West's Syndrome."

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