During a seizure, a large group of brain cells fire electrical signals simultaneously and uncontrollably, overwhelming the brain’s normal communication patterns. This surge of synchronized activity can alter consciousness, trigger involuntary movements, change sensations, or all three at once. Roughly 8% to 10% of people will experience at least one seizure in their lifetime, and what happens during each one depends on where in the brain the abnormal firing starts and how far it spreads.
What Happens Inside the Brain
Under normal conditions, brain cells communicate through carefully timed electrical and chemical signals. During a seizure, two things go wrong at once: neurons begin firing in rapid, high-frequency bursts, and large populations of those neurons lock into sync with each other. The result is a massive wave of electrical activity that overwhelms the brain’s usual checks and balances.
The brain relies on a balance between signals that excite neurons and signals that calm them down. The main excitatory chemical messenger ramps up activity, while the main inhibitory one dampens it. In a seizure, that balance tips sharply toward excitation. Too much excitatory signaling and too little inhibitory signaling allows neurons to fire unchecked, which can spread the abnormal activity to neighboring brain regions or, in some cases, across the entire brain. This runaway excitation can also damage or kill neurons if it continues long enough.
The Four Phases of a Seizure
Not every seizure follows all four phases, and many come on suddenly with no warning at all. But when warning signs do appear, they tend to follow a predictable sequence.
Prodrome
Hours or even days before a seizure, some people notice subtle changes: mood shifts, difficulty concentrating, lightheadedness, or trouble sleeping. These aren’t part of the seizure itself but can serve as early warning signs that one is approaching.
Aura
An aura occurs in the seconds or minutes just before the seizure’s main event. It can involve flashing lights or visual distortions, a sudden metallic or bitter taste, an unexpected smell, tingling on the skin, or a wave of anxiety or fear. Technically, an aura is itself a small focal seizure, which is why the sensations feel so vivid and strange. Many people never experience an aura, while others recognize theirs reliably enough to prepare before the seizure progresses.
Ictal Phase
This is the seizure itself, the period of active abnormal electrical firing. What it looks like from the outside varies enormously depending on the type of seizure (covered in the next sections). It can last a few seconds to several minutes.
Postictal Phase
Once the electrical storm subsides, the brain doesn’t snap back to normal immediately. The postictal phase typically lasts 5 to 30 minutes but can stretch much longer. Common experiences include confusion, extreme drowsiness, headache, nausea, and strong emotions like fear or sadness. Speech, movement, and memory are all affected during this window. About 30% of people have no memory of their seizure at all, and only about a quarter remember all of their seizures.
Some people experience temporary weakness on one side of the body afterward, which can take one to two days to resolve. Others develop brief episodes of repetitive, purposeless movements like nose-wiping or spitting. In some cases, cognitive fog, mood changes, and low energy can linger for days. Brain wave activity, as measured on an EEG, takes an average of two hours to return to its baseline pattern, though it can take up to seven hours.
Focal Seizures: Starting in One Area
Focal seizures begin in a specific region of one side of the brain. What you experience depends entirely on which region is involved. A focal seizure in the area that processes vision might cause flashing lights. One in a motor area might cause one arm or one side of the face to jerk rhythmically.
In a focal aware seizure, you remain conscious throughout. You know something strange is happening, you can hear people around you, but you can’t necessarily stop the unusual sensations or movements. These episodes often last under two minutes.
In a focal impaired awareness seizure, consciousness is partially or fully disrupted. You may stare blankly and perform repetitive, purposeless actions called automatisms: lip smacking, chewing motions, picking at clothing, rubbing your hands together, or making small hand movements. Seizures originating in the frontal lobes can produce more dramatic automatisms like bicycling leg movements or pelvic thrusting. People in the middle of these seizures typically don’t respond when spoken to and won’t remember the episode afterward.
Generalized Seizures: Both Sides at Once
Generalized seizures engage networks on both sides of the brain from the very start. They come in several forms, and the two most recognized are tonic-clonic seizures and absence seizures.
Tonic-Clonic Seizures
These are what most people picture when they think of a seizure. The tonic phase comes first: the body stiffens, sometimes beginning with a sudden cry or scream as air is forced past the vocal cords. The person loses consciousness and falls. The skin may turn bluish because the chest muscles tighten and temporarily interfere with breathing.
The clonic phase follows within seconds. The stiffness gives way to rhythmic jerking of the arms, legs, and face. This phase typically lasts one to three minutes. Afterward, the person enters the postictal phase, often deeply confused, exhausted, and sleepy. Muscle soreness is common because of the intense, involuntary contractions.
Absence Seizures
At the other end of the spectrum, absence seizures are brief, sudden lapses in consciousness that look nothing like a tonic-clonic episode. The person simply stops what they’re doing and stares blankly for a few seconds, sometimes with subtle eyelid fluttering, lip smacking, chewing motions, or small finger movements. There’s no falling, no jerking, no cry. These seizures are easily mistaken for daydreaming, especially in children, and can happen dozens of times a day before anyone notices a pattern.
When a Seizure Becomes an Emergency
Most seizures end on their own within a few minutes. A seizure becomes a medical emergency when it lasts five minutes or longer without stopping, or when seizures occur back to back without the person recovering in between. This condition, called status epilepticus, requires immediate treatment because prolonged uncontrolled electrical firing can cause permanent brain injury. The five-minute threshold replaced an older 30-minute definition because waiting that long increased the risk of serious harm.
What Bystanders Actually See
From the outside, a seizure can look dramatically different depending on its type. A tonic-clonic seizure is unmistakable: a person falls, stiffens, and jerks. But many seizures are far subtler. Someone having a focal impaired awareness seizure may simply appear “zoned out,” fidgeting with their clothes or smacking their lips. A person having an absence seizure may pause mid-sentence for a few seconds and then resume as if nothing happened. Some seizures produce no visible movement at all, only an internal experience of strange sensations, emotions, or altered awareness that the person may struggle to describe afterward.
The wide range of possible presentations is one reason seizures often go unrecognized. A child staring off in class, an adult who briefly “checks out” during conversation, or someone who reports sudden unexplained smells or tastes may all be experiencing seizure activity without anyone, sometimes including the person themselves, realizing it.