A seizure is a burst of uncontrolled electrical activity in the brain that temporarily changes how you move, feel, behave, or think. Up to 10% of people worldwide will experience at least one seizure during their lifetime, according to the World Health Organization. Most seizures last from a few seconds to a couple of minutes and stop on their own, but understanding what’s happening in the brain, what different seizures look like, and how to respond can make a real difference.
What Happens in the Brain During a Seizure
Your brain runs on electrical signals. Billions of neurons fire in organized patterns, communicating through a careful balance of chemicals that either excite or calm neighboring cells. During a seizure, that balance breaks down. Neurons begin firing inappropriately and in sync, like a crowd that suddenly starts clapping in unison instead of at their own pace. This synchronized wave of electrical activity overwhelms the brain’s normal rhythms and produces the physical or mental symptoms you can see from the outside.
The two key chemical players are glutamate, which excites neurons and tells them to fire, and GABA, which inhibits neurons and tells them to quiet down. Seizures happen when the excitatory side overpowers the inhibitory side. Once that firing crosses a certain threshold, it amplifies rapidly, recruiting large populations of neurons into the abnormal discharge. The specific symptoms depend on where in the brain this electrical storm starts and how far it spreads.
Focal Seizures: Starting in One Area
Focal seizures begin in a specific region of the brain, and their symptoms reflect whatever that region normally controls. A focal seizure in the area responsible for vision might cause flashing lights; one in a movement area might cause a hand or arm to jerk rhythmically.
There are two main types. In a focal aware seizure, the person stays conscious but experiences unusual sensations: a strong feeling of déjà vu, a strange rising sensation in the stomach, or involuntary movements in one part of the body. These episodes are sometimes called “auras,” and some people with epilepsy recognize them as warnings that a larger seizure may follow.
In a focal impaired awareness seizure, consciousness is affected. The person may appear dazed or confused, stare blankly, smack their lips, or pick at their clothes. They typically can’t respond to questions or follow directions for a few minutes and often don’t remember the episode afterward. To a bystander, it can look like the person simply “zoned out,” which is why these seizures sometimes go unrecognized.
Generalized Seizures: Affecting the Whole Brain
Generalized seizures involve abnormal electrical activity across both sides of the brain from the start. They tend to produce more dramatic symptoms and almost always involve some loss of awareness.
The most recognizable type is the tonic-clonic seizure (formerly called grand mal). It has two phases: a tonic phase where the muscles stiffen and the person may cry out and fall, followed by a clonic phase of rhythmic jerking throughout the body. These seizures typically last one to three minutes.
Other types of generalized seizures are subtler. Absence seizures cause brief staring spells, sometimes with rapid blinking or small chewing motions, lasting only a few seconds. They’re especially common in children and can happen dozens of times a day without anyone noticing. Myoclonic seizures produce quick, lightning-fast jerks, often in the arms or upper body. Atonic seizures cause a sudden loss of muscle tone, making a person drop to the ground without warning, which is why they’re sometimes called “drop attacks.”
The Four Phases of a Seizure
Not every seizure follows the same script, but many move through four distinct phases. The prodrome can begin hours or even days before a seizure, showing up as mood changes, irritability, headaches, or a vague sense that something is “off.” Not everyone experiences this phase, but those who do often learn to recognize it as an early signal.
The aura marks the actual start of electrical disruption in the brain. It may involve odd smells, tastes, visual disturbances, or an intense emotional feeling. Technically, an aura is itself a small focal seizure. The ictus is the main event: the period of active seizure symptoms, whether that’s convulsions, staring, or involuntary movements. After the electrical storm subsides, the postictal phase begins. Recovery can take minutes to hours, and the person may feel confused, exhausted, sore, or emotionally fragile. Some people experience temporary difficulty speaking or weakness on one side of the body.
Common Causes and Triggers
Seizures have a long list of possible causes, and the most likely ones shift depending on age. In newborns, birth complications, oxygen deprivation, and metabolic imbalances are the primary culprits. In young children, febrile seizures triggered by high fever are extremely common and usually harmless. In adults, head injuries, brain tumors, stroke, and infections like meningitis are frequent causes. In older adults, stroke and neurodegenerative diseases become more prominent.
A single seizure doesn’t necessarily mean epilepsy. Seizures can be provoked by specific, temporary conditions: very low blood sugar, severe dehydration, alcohol withdrawal, certain medications, or extreme sleep deprivation. These “provoked” seizures may never return once the underlying trigger is removed. Epilepsy is diagnosed when someone has recurrent, unprovoked seizures, indicating an ongoing tendency of the brain to generate them.
Seizures That Aren’t Electrical
Some episodes look exactly like seizures but don’t involve abnormal electrical activity in the brain. These are called psychogenic nonepileptic seizures (PNES), and they’re more common than many people realize. PNES episodes are real and involuntary, not faked, but they’re driven by psychological distress rather than electrical misfiring.
Certain features can suggest PNES rather than epileptic seizures: eyes that stay closed throughout the episode, out-of-sync limb movements, side-to-side head shaking, pelvic thrusting, or convulsive episodes lasting longer than 10 minutes. Some people retain awareness during what looks like a full-body convulsion, which is unusual in epileptic tonic-clonic seizures. The definitive way to tell the difference is video EEG monitoring, which records brain waves during an episode. Normal electrical activity during a seizure-like event points toward PNES; abnormal activity confirms epilepsy.
How Seizures Are Diagnosed
An EEG is the primary tool for evaluating seizures. It measures electrical activity across the brain through sensors placed on the scalp and can reveal the type and location of abnormal patterns even between seizures. In some cases, extended video EEG monitoring over several days is used to capture an actual episode on camera while simultaneously recording brain waves. This is especially helpful for seizures that are subtle or infrequent.
Brain imaging plays a complementary role. An MRI provides a detailed look at the brain’s structure, helping doctors spot potential causes like tumors, scarring, or developmental abnormalities. A functional MRI can map critical areas for speech and movement, which becomes important if surgery is ever considered. Blood tests check for infections, blood sugar problems, electrolyte imbalances, and genetic conditions that may be contributing. Wearable devices that detect the characteristic movements of tonic-clonic seizures are now FDA-cleared and can help track seizure frequency in daily life.
What to Do if Someone Has a Seizure
If you witness someone having a convulsive seizure, your most important job is keeping them safe, not stopping the seizure. Ease the person to the ground if they’re falling. Gently turn them onto one side with their mouth pointing downward so their airway stays clear. Clear away nearby furniture or hard objects, place something soft under their head, remove their glasses, and loosen anything tight around their neck.
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, including your fingers. The old idea about “swallowing the tongue” is a myth, and forcing objects between the teeth can cause real injury. Don’t attempt mouth-to-mouth breathing during the seizure; breathing typically resumes on its own once it ends. Don’t offer food or water until the person is fully alert.
Time the seizure from the moment it starts. If it lasts longer than five minutes, or if seizures repeat without the person regaining consciousness in between, that’s a medical emergency called status epilepticus. It requires immediate help because prolonged seizure activity can cause brain damage. A seizure in someone who has never had one before, or one that occurs alongside a head injury, high fever, or pregnancy, also warrants emergency care.