A seizure is a burst of uncontrolled electrical activity in the brain that temporarily changes how you move, feel, or behave. It happens when large groups of brain cells fire at the same time in an abnormal, synchronized pattern, overwhelming the brain’s normal signaling. Seizures are more common than most people realize: roughly 8% to 10% of people will experience at least one seizure during their lifetime.
What Happens in the Brain During a Seizure
Your brain cells communicate through small electrical impulses that fire in orderly sequences. During a seizure, two things go wrong simultaneously: neurons start firing in rapid, high-frequency bursts, and large populations of those neurons become locked in sync with each other. This hypersynchronized firing drowns out normal brain activity the way a stadium crowd chanting in unison drowns out individual conversations.
Several things can trigger this runaway electrical activity. The brain’s excitatory signals (which tell neurons to fire) may become too strong, or its inhibitory signals (which tell neurons to quiet down) may become too weak. Changes in the channels that control how charged particles like sodium and calcium move in and out of brain cells can also tip the balance toward uncontrolled firing. The result is a cascade: calcium floods into neurons, which opens sodium channels, which triggers a rapid chain of electrical discharges that spread across part or all of the brain.
Types of Seizures
Seizures fall into a few broad categories based on where in the brain the abnormal activity starts and how far it spreads.
Focal Seizures
Focal seizures begin in one specific area of the brain. What they look and feel like depends on which area is affected. You might experience a strange sensation, a wave of fear, a jerking movement in one arm, or a brief altered awareness where you stare blankly and don’t respond. Some focal seizures stay contained; others spread to become full-body convulsions.
Generalized Seizures
Generalized seizures involve both sides of the brain from the start. The most dramatic type, the tonic-clonic seizure (sometimes called a grand mal), begins with a sudden loss of consciousness. During the tonic phase, the body stiffens. The person may let out a cry as air is forced past tense vocal cords. This gives way to the clonic phase: rhythmic jerking of the arms and legs. The whole episode typically lasts one to three minutes. Tongue biting occurs in about 22% of cases, and some people lose bladder control as muscles relax afterward.
Absence seizures are a much subtler form of generalized seizure. They cause a brief vacant stare lasting around 10 seconds, sometimes up to 30 seconds. You might notice lip smacking, eyelid fluttering, or small hand movements. The person doesn’t fall, and there’s no confusion afterward. They simply resume what they were doing, often unaware anything happened. Some people, especially children, experience dozens of these episodes per day.
Unknown Seizures
When a seizure wasn’t witnessed from the beginning, or when test results are inconclusive, it gets classified as “unknown whether focal or generalized.” This is a placeholder category that can be updated once more information is available.
Common Causes by Age
What triggers a first seizure often depends on how old you are. In children, high fevers are one of the most common causes (febrile seizures), along with genetic conditions and infections. In young adults between roughly 13 and 35, brain infections are the leading cause, followed by tumors and metabolic problems like dangerously low blood sugar or sodium levels. Stroke is essentially absent as a seizure trigger in this age group.
That changes dramatically in middle age. Between 36 and 55, stroke becomes the dominant cause, responsible for about 37% of new-onset seizures. In adults over 55, stroke accounts for more than 80% of new seizures. Other causes at any age include head injuries, alcohol withdrawal, drug use, sleep deprivation, and autoimmune conditions that cause the immune system to attack brain tissue.
How Seizures Are Diagnosed
After a first seizure, the main goals are to figure out what type it was and what caused it. The process usually starts with a neurological exam, where a provider tests your reflexes, coordination, and mental function. Two key tests follow from there.
An EEG (electroencephalogram) records your brain’s electrical patterns through small sensors placed on your scalp. It’s the most important tool for confirming seizure activity and identifying the seizure type. An MRI scan takes detailed images of the brain’s structure to look for anything that could be triggering seizures, like scar tissue, a tumor, or damage from a past stroke. In children, and sometimes in adults, genetic testing may also be useful to identify inherited conditions that raise seizure risk.
The Recovery Phase After a Seizure
The period immediately after a seizure is called the postictal state. It’s the brain’s reboot process, and it can feel rough. The most common symptoms are exhaustion, confusion, headache, sore muscles, and trouble remembering what happened. Some people experience mood changes including anxiety, agitation, or depression. Difficulty speaking is also common, particularly after larger seizures.
How long this recovery takes varies widely. After an absence seizure, there’s typically no postictal phase at all. After a tonic-clonic seizure, confusion and fatigue can last anywhere from a few minutes to several hours, and some people feel off for a full day or more. There’s no way to speed up this process. Rest, quiet, and reassurance are the most helpful things during recovery.
How to Help Someone Having a Seizure
If you witness a seizure, what you do (and don’t do) in those moments matters. The CDC recommends these steps:
- Stay with the person and keep calm.
- Move hazards away from them, not the other way around.
- If they’re on the ground, gently roll them onto their side with their mouth pointing downward so their airway stays clear.
- Place something soft (a folded jacket, for example) under their head.
- Loosen anything tight around their neck, and remove their glasses if they’re wearing them.
- Time the seizure. If it lasts longer than 5 minutes, call 911.
- Once it’s over, help them sit somewhere safe, explain calmly what happened, and offer to help them get home.
Equally important is what not to do. Don’t hold the person down or try to restrain their movements. Don’t put anything in their mouth, as this can damage teeth or the jaw. Don’t attempt mouth-to-mouth breathing during the seizure, since people almost always resume breathing on their own. Don’t offer food or water until the person is fully alert, because swallowing is unreliable during the postictal phase.
When a Seizure Is an Emergency
A single seizure in someone with known epilepsy isn’t always cause for a 911 call, but certain situations are. Call for emergency help if the seizure lasts longer than 5 minutes, if a second seizure follows the first without the person regaining awareness, if the person doesn’t start breathing normally afterward, if they’re injured during the seizure, if it happens in water, or if it’s their first seizure ever. Seizures during pregnancy also warrant immediate emergency care.