A seizure is a sudden burst of abnormal electrical activity in the brain, while a convulsion is uncontrolled shaking of the body as muscles repeatedly tighten and relax. A seizure can cause a convulsion, as it does in a tonic-clonic seizure. Many seizures never cause shaking, though, and some convulsions come from fainting or other causes with no seizure involved.
| Seizure with convulsion | Seizure without convulsion | Convulsive syncope | Functional seizure | |
| What is happening | Abnormal electrical activity spreads across the brain | Abnormal electrical activity stays brief or limited to one area | Blood flow to the brain drops for a moment, with no seizure activity | No abnormal electrical activity in the brain |
| What others see | Stiffening, a fall, rhythmic jerking, loss of consciousness | A blank stare, confusion, repetitive movements, or nothing visible | A faint followed by a few seconds of jerking | Can resemble any seizure type, including full-body shaking |
| How long it lasts | Usually one to three minutes | Seconds to a few minutes | Less than a minute | Varies |
| Afterward | Confusion and tiredness, sometimes for an hour or more | Often a quick return to normal, sometimes brief confusion | Awareness returns quickly | Varies |
Seizures That Cause Convulsions
A tonic-clonic seizure, once called a grand mal seizure, is the seizure type that produces a full convulsion. During the tonic (stiffening) phase, the person loses consciousness and the body goes rigid, which causes a fall if they are standing. The clonic (jerking) phase follows with rhythmic movement of the arms and legs, the convulsion itself. The active part generally lasts one to three minutes, according to the Epilepsy Foundation.
Some tonic-clonic seizures begin in one area of the brain before spreading to both sides. The person may notice a warning first, such as a strange smell or a sudden sense of déjà vu, while still fully aware. Afterward, confusion and sleepiness can last from several minutes to an hour or more. A bitten tongue or cheek, sore muscles, and loss of bladder control are also common, and a witness who notices any of them has information a doctor will want.
Seizures Without Convulsions
An absence seizure causes no shaking at all, only a blank stare lasting a few seconds, often without the person realizing anything happened. A focal seizure can stay limited to one part of the brain, producing a brief stretch of confusion, repetitive movements such as lip smacking, or sensations only the person feels.
Even without shaking, each of these events is abnormal electrical activity in the brain and deserves the same evaluation from a seizure specialist as a convulsive seizure. Because they are easy to miss or mistake for daydreaming, seizures without convulsions can go unrecognized for a long time.
Convulsions Without a Seizure
Convulsive syncope is a convulsion with no seizure behind it, a faint followed by a few seconds of jerking as blood flow to the brain briefly drops. It can look like a seizure to anyone watching, yet no seizure activity is involved and awareness returns quickly. Fainting can also come from a heart rhythm problem, which is why an evaluation for loss of consciousness sometimes includes a heart check alongside neurological testing.
Functional seizures, also called psychogenic non-epileptic seizures, can resemble any seizure type, full-body shaking included, yet no abnormal electrical activity occurs in the brain during them. The episodes are real and not under the person’s control. Many people who have them also live with stress, anxiety, or past trauma. Antiseizure medications do not help, while psychological therapy, most often cognitive behavioral therapy (CBT), is the main treatment.
How Doctors Tell if a Convulsion Was a Seizure
A detailed account from the person and anyone who saw it often points toward a seizure, a faint, or a functional episode. How the episode started, what the person was doing just before, how long the shaking lasted, and how quickly they came back all shape which tests come next.
Blood work checks for triggers such as very low blood sugar or an electrolyte imbalance. A seizure set off by an acute cause like that, or by alcohol withdrawal, is called a provoked seizure. It is a true seizure rather than epilepsy, and it usually does not return once the trigger is treated.
A brain MRI looks for structural causes, such as scarring or an old injury. An EEG test records the brain’s electrical activity and can pick up patterns linked to seizures, although a normal result on its own does not rule them out. The same evaluation applies after a single unexplained episode and when convulsions keep returning.
When to Call 911 for a Seizure or Convulsion
A seizure lasting more than five minutes, or repeated seizures without recovery in between, is a medical emergency. Call 911. The medical term is status epilepticus, a seizure that does not stop on its own and needs emergency treatment.
The Epilepsy Foundation also advises calling 911 when any of these apply:
- It is the person’s first seizure
- The person is injured or is not returning to their usual state
- The person is pregnant
- The seizure happens in water
When to See an Epileptologist for Convulsions
When convulsions keep returning or testing leaves the cause unclear, an epileptologist, a neurologist with fellowship training in seizure disorders, is trained to sort seizures from the events that imitate them. Omar Moore, MD is a board-certified neurologist and fellowship-trained epileptologist based in Jacksonville, Florida, who sees patients statewide by telehealth. He completed fellowship training in Epilepsy and Clinical Neurophysiology at the University of Illinois in Chicago, the sub-specialty built around reading EEGs and diagnosing seizure disorders.
Appointments can happen by video from anywhere in Florida. When an EEG is needed, a technician sets up the equipment in your home and returns to remove it. Blood work and imaging are referred to facilities near you, with results coming back to Dr. Moore.
Find Out Whether It Was a Seizure With NeuroDoc
Dr. Omar Moore, MD is a fellowship-trained epileptologist at NeuroDoc who helps patients across Florida find out whether an episode was a seizure, a faint, or something else. Visits can take place by telehealth, and if an EEG is needed, it is recorded in your own home instead of a hospital lab. Call (904) 204-6585 or submit an online appointment request, and the practice will be in touch within 48 hours.
Seizure vs Convulsion FAQs
Is Convulsive Syncope a Seizure?
Convulsive syncope is not a seizure. It is fainting with a few seconds of jerking, caused by a brief drop in blood flow to the brain rather than abnormal electrical activity. It often follows standing up quickly, dehydration, or the sight of blood, and awareness returns quickly. A doctor should still evaluate it, since some fainting comes from heart rhythm problems.
Does a Seizure or Convulsion Mean Epilepsy?
A single seizure or convulsion does not mean epilepsy on its own. Under the International League Against Epilepsy definition, epilepsy is diagnosed after two unprovoked seizures more than 24 hours apart, or after one unprovoked seizure when the chance of another within 10 years is at least 60%. A provoked seizure does not count toward epilepsy, and a convulsion from fainting is not a seizure at all.
Can an EEG Tell if You Had a Seizure?
An EEG shows a seizure directly only if one happens during the recording. Between seizures, it can pick up patterns that point to a seizure tendency, but a single routine EEG after a first seizure often comes back normal, even in people later diagnosed with epilepsy. Longer recordings, such as a 24-hour EEG worn at home, catch those patterns more often than a standard short test.
Do I Need to See a Doctor After One Convulsion?
A doctor should evaluate any convulsion, even if the person feels fine afterward and even if it turns out not to be a seizure. Possible causes range from a simple faint to a heart rhythm problem or epilepsy, and an evaluation identifies which one it was. Once any emergency has passed, telehealth makes that evaluation possible from anywhere in Florida.
