A seizure is a burst of uncontrolled electrical activity in the brain that temporarily disrupts how the body functions. What it actually does depends on where in the brain the activity starts and how far it spreads, but the effects range from brief staring spells lasting a few seconds to full-body convulsions, loss of consciousness, and changes in heart rate, breathing, and blood pressure. Repeated seizures over time can cause measurable damage to brain structure and memory.
What Happens Inside the Brain
Under normal conditions, brain cells fire in coordinated but independent patterns. During a seizure, a large group of neurons begin firing together in rapid, synchronized bursts. This hypersynchronization is the core problem. It can start in a small, specific area of the brain and stay there, or it can spread outward to neighboring regions and eventually involve both sides of the brain at once.
The electrical imbalance comes down to two types of chemical signals in the brain. One type (driven by glutamate) excites neurons and makes them more likely to fire. The other type (driven by GABA) calms neurons down and prevents excessive firing. During a seizure, excitatory signaling overwhelms the brain’s ability to inhibit it. The receptors that normally respond to calming signals decrease in number or become desensitized, while excitatory receptors increase. The result is a runaway chain reaction of electrical activity that the brain temporarily cannot shut down.
What Seizures Look Like From the Outside
Not all seizures involve shaking or convulsions. What a seizure does to the body depends on its type.
Focal Seizures
Focal seizures start on one side of the brain and may affect only one side of the body. In a focal aware seizure, a person stays conscious but might feel a sudden wave of déjà vu, a strange sensation in their stomach, or have involuntary movements in one hand or arm. In a focal impaired awareness seizure, the person looks dazed or confused. They may smack their lips, pick at their clothing, or be unable to respond to questions for several minutes.
Generalized Seizures
Generalized seizures involve both sides of the brain from the start and almost always cause a loss of consciousness. The most dramatic form is the tonic-clonic seizure (sometimes called grand mal). It begins with a tonic phase: the muscles throughout the body stiffen, sometimes starting with a sudden cry as air is forced past the vocal cords. The person may fall to the ground and turn blue from temporarily stopped breathing. This transitions into the clonic phase, where the muscles jerk rhythmically on both sides of the body. Bladder control can be lost, and tongue biting is common.
Other generalized seizures are far less visible. Absence seizures, most common in children, cause a blank stare and a brief pause in activity lasting 4 to 30 seconds. A child might stop mid-sentence, blink rapidly or flutter their eyelids, and then resume what they were doing with no memory of the pause. These can happen 10 to 30 times a day and are often mistaken for daydreaming. Unlike tonic-clonic seizures, absence seizures have no warning aura and no confusion afterward.
Other types include myoclonic seizures (quick, lightning-fast jerks of the limbs), tonic seizures (sudden full-body stiffness without the jerking phase), and atonic seizures (a sudden, complete loss of muscle tone that causes a person to collapse).
What Seizures Do to the Heart and Lungs
Seizures don’t just affect the brain. They trigger the body’s fight-or-flight system, and the cardiovascular effects are significant. More than 85% of complex partial and tonic-clonic seizures cause a rapid heart rate. In some cases, the heart rate spikes roughly 13 seconds before the seizure even shows up on a brain monitor, meaning the body’s stress response fires before the electrical storm fully develops.
Blood pressure rises, pupils dilate, and the face may flush. Breathing is also disrupted. Brief pauses in breathing (apnea) are common during many seizures, and prolonged pauses with visible blueness of the skin occur during tonic-clonic and sustained tonic seizures. In rare cases (fewer than 2% of seizures), the opposite happens: heart rate drops and blood pressure falls, which can cause fainting on top of the seizure itself. These cardiovascular disruptions are one reason prolonged seizures can be life-threatening.
The Recovery Phase After a Seizure
The period immediately after a seizure, called the postictal state, is often as disorienting as the seizure itself. It typically lasts 5 to 30 minutes but can stretch much longer. Common symptoms include confusion, drowsiness, headache, nausea, and excessive saliva. Some people experience temporary weakness on one side of the body, which can take one to two days to fully resolve.
Brain wave activity takes an average of two hours to return to normal after a seizure, and in some cases up to seven hours. Cognitive effects, mood changes, and low energy can linger for days. Postictal delirium, when it occurs, typically lasts hours but may continue for one to two days. Absence seizures are the exception: they end abruptly with no postictal phase, and the person immediately returns to normal.
Long-Term Effects on the Brain
A single seizure does not necessarily cause lasting harm, but repeated seizures over time can leave a measurable mark on brain structure and function. The hippocampus, the brain region most critical for forming new memories, is particularly vulnerable. Animal studies show that neuronal loss begins after as few as three generalized tonic-clonic seizures and progresses with each additional seizure. After 150 seizures, cell loss in key areas of the hippocampus reached 54% to 82%, a pattern that resembles the type of scarring seen in people with chronic, difficult-to-treat epilepsy.
Memory and thinking are affected in parallel. Spatial memory problems have been detected after as few as six focal seizures and 30 generalized tonic-clonic seizures. Over longer timelines, studies tracking patients for a median of 13 years found that greater numbers of generalized seizures were linked to declining verbal IQ, performance IQ, verbal learning and memory, and language fluency. A large controlled study of people with childhood-onset temporal lobe epilepsy found that their cognitive abilities stayed below those of matched controls for decades, with an implied earlier onset of age-related cognitive decline later in life.
The structural changes go beyond the hippocampus. Widespread cortical thinning, a reduction in the brain’s outer layer, was found in 77% of epilepsy patients in one study, with the annual rate of thinning roughly double what would be expected from normal aging. This thinning was most pronounced in adults over 55 and during the first five years after seizures began. Epilepsy lasting more than 20 years was associated with declines in intelligence, verbal memory, and the brain’s ability to generate new neurons in the hippocampus.
When a Seizure Becomes an Emergency
Most seizures stop on their own within one to three minutes. A seizure becomes a medical emergency, called status epilepticus, when it lasts five minutes or longer without stopping, or when seizures occur back-to-back without the person recovering consciousness between them. At this point, the brain’s ability to self-correct has failed, and the risk of lasting brain damage, cardiovascular collapse, and death rises sharply with each passing minute. Roughly 10 to 20% of people with epilepsy will experience at least one episode of status epilepticus in their lifetime.
Even outside of emergencies, the cardiovascular strain of repeated seizures carries long-term risk. Sudden unexpected death in epilepsy (SUDEP) is linked to seizure-related breathing pauses and fluid buildup in the lungs, and is the leading cause of death in people with uncontrolled epilepsy. The risk is highest in people who have frequent generalized tonic-clonic seizures, particularly during sleep.