When you have a seizure, your brain’s electrical activity suddenly becomes disorganized, causing a surge of uncontrolled signals that can affect your body, awareness, and senses in ways that range from barely noticeable to dramatic full-body convulsions. Roughly 8% to 10% of people will experience at least one seizure in their lifetime, so this is far from rare. What actually happens during those seconds or minutes depends on which parts of the brain are involved and how far the abnormal activity spreads.
What Goes Wrong in the Brain
Your brain cells communicate through a careful balance of excitatory and inhibitory chemical signals. During a seizure, that balance collapses. The brain floods with glutamate, a chemical that stimulates neurons to fire, while the signals that normally act as brakes become weaker. The result is a runaway chain reaction: large groups of neurons begin firing in sync, overwhelming normal brain circuits.
This synchronized misfiring is what produces every symptom you feel or see during a seizure. If the surge stays in one area, you might only notice odd sensations on one side of your body. If it spreads across the entire brain, you lose consciousness and your muscles seize up. During prolonged seizures, the overstimulation can actually damage neurons by flooding them with calcium, which is why stopping a long seizure quickly matters so much.
Warning Signs Before a Seizure
Some people get an early warning called a prodrome, hours or even a day before a seizure hits. The most common signs are irritability, mood changes, headaches, or a vague sense that something is about to happen. Interestingly, a small percentage of people experiencing a prodrome are actually having low-level seizure activity in the brain during that time without realizing it.
Closer to the event, some people experience an aura, which is technically the very beginning of the seizure itself. Auras vary widely depending on which brain region is involved. People with seizures originating in the temporal lobe commonly describe a rising sensation in the stomach, a sudden feeling of déjà vu, or the opposite: feeling like a familiar place is completely foreign. Others hear ringing, notice voices sounding far away, or see things that aren’t there. Not everyone gets auras, but for those who do, they can serve as a few seconds of warning.
What Happens During a Major Convulsive Seizure
The type most people picture when they hear “seizure” is the generalized tonic-clonic seizure, which involves the whole brain from the start. It typically begins with an abrupt loss of consciousness. There’s no aura, no gradual buildup. The person may let out a cry or scream as air is forced out of their lungs by sudden muscle contraction. This is involuntary and doesn’t mean they’re in pain.
The tonic phase comes first: every muscle in the body stiffens. The person falls rigid, sometimes turning slightly blue because the chest muscles lock up and breathing temporarily stops. This phase usually lasts 10 to 20 seconds.
Then comes the clonic phase: rhythmic jerking of the arms, legs, and sometimes the face. The jaw may clench hard enough to bite the side of the tongue, which happens in about 22% of cases. Saliva can pool or froth at the mouth because the person can’t swallow. Some people lose bladder control as the sphincter muscles relax. The whole convulsive episode typically lasts one to three minutes.
Seizures That Don’t Involve Shaking
Not all seizures look dramatic. Absence seizures cause a sudden blank stare, sometimes mistaken for daydreaming or a lapse in attention. The person stops what they’re doing mid-sentence or mid-action without falling. You might notice subtle signs: eyelid fluttering, lip smacking, chewing motions, or small repetitive finger movements. These episodes usually last only a few seconds, and the person often has no memory of them afterward.
Focal seizures that stay on one side of the brain can look different still. In focal aware seizures, the person remains conscious the whole time but may feel tingling on one side of the body, experience sudden fear or a sense of doom, or notice involuntary twitching in one hand or one side of the face. They can sometimes talk through it and remember everything. Focal seizures with impaired awareness are different: the person appears awake but becomes unresponsive, may stare blankly, and often makes automatic movements like picking at clothing or smacking their lips. They typically won’t remember the episode.
Any focal seizure can spread to involve the whole brain, at which point it becomes a full convulsive seizure.
What Happens to Your Heart and Breathing
Seizures don’t just affect the brain. In over 90% of complex partial and tonic-clonic seizures, heart rate spikes above 100 beats per minute, often with a steep acceleration right at the onset. The heart may also develop brief rhythm irregularities. One study of patients with hard-to-control focal epilepsy found that 39% had abnormal heart rhythms during or immediately after seizures.
A dangerous slowing of the heart is rare, occurring in well under 1% of monitored cases, and it tends to happen alongside breathing changes, particularly brief pauses in breathing. This combination of cardiac and respiratory disruption during seizures is one reason researchers believe prolonged seizures can, in rare cases, be fatal. Oxygen levels can drop during the convulsive phase because the chest muscles are too rigid to breathe normally, though they typically recover once the jerking stops.
The Recovery Period
The postictal state, the recovery phase after a seizure, is often the most disorienting part of the experience. It typically lasts 5 to 30 minutes, though it can stretch much longer depending on the seizure type and severity. During this time, the brain is essentially rebooting. Common symptoms include confusion, drowsiness, headache, nausea, and sore muscles from the sustained contractions.
The specific deficits depend on which brain areas were involved. If the seizure affected language areas, the person may slur words or struggle to form sentences. If motor areas were involved, they may temporarily be unable to move an arm or leg, a phenomenon called Todd’s paralysis that can last hours or even one to two days. About 30% of people have no memory of the seizure at all, and only a quarter remember all of their seizures.
For focal seizures with impaired awareness, postictal symptoms often clear within one to two hours. But some people experience lingering effects on mood, cognition, and energy levels that persist for days. In rare cases, particularly with temporal lobe seizures, a person can develop postictal psychosis hours to a day after the seizure: hallucinations, paranoia, and delusions that may last several days and require treatment. Brain wave activity itself takes an average of two hours to return to normal, though it can take up to seven hours.
When a Seizure Becomes an Emergency
Most seizures end on their own within a few minutes. The critical threshold is five minutes. A seizure lasting longer than five minutes, or multiple seizures without a return to normal consciousness between them, is called status epilepticus. This is a medical emergency because the prolonged surge of excitatory brain chemicals can cause permanent neuronal damage. Call 911 if a seizure crosses that five-minute mark.
What to Do if Someone Is Seizing
If you’re with someone having a convulsive seizure, the priority is preventing injury, not stopping the seizure. Move them only if they’re in immediate danger, like near a road or a hot stove. Cushion their head if they’re on the ground and loosen any tight clothing around their neck. Do not put anything in their mouth, including your fingers. Despite the old myth, a person cannot swallow their tongue during a seizure, and forcing something between clenched jaws risks breaking teeth or injuring you both.
Once the convulsions stop, turn them onto their side to keep the airway clear. Stay with them through the postictal phase. They’ll likely be confused and disoriented, and having someone calmly explain what happened can make a significant difference as they come around. Time the seizure from the start if you can, because that information is one of the most useful things you can give to medical responders or the person’s doctor.