A grand mal seizure, now called a tonic-clonic seizure in medical terminology, is a type of seizure that causes loss of consciousness, full-body muscle stiffening, and violent rhythmic jerking. It’s the type most people picture when they think of a seizure. The entire event typically lasts one to three minutes, but the recovery period afterward can stretch from 30 minutes to several hours.
Why Doctors Say “Tonic-Clonic” Now
The term “grand mal” (French for “great sickness”) was used for decades, and you’ll still hear it in everyday conversation. The medical community shifted to “tonic-clonic” because the name actually describes what happens during the seizure: a tonic phase (muscles stiffen) followed by a clonic phase (muscles jerk rhythmically). The older term didn’t convey any useful clinical information, so it was replaced to be more precise.
What It Looks and Feels Like
Some people experience a warning, called an aura, seconds to minutes before the seizure spreads across the brain. This might be a sudden strange smell, a wave of nausea, an unusual sensation in part of the body, or the eyes and head turning forcefully to one side. The person is still fully aware during this brief window. Not everyone gets an aura, though. When the seizure starts without warning, it hits all at once.
The Tonic Phase
The seizure often begins with a sudden cry or groan, not from pain or fear, but from air being forced out of the lungs as all the muscles contract at once. The entire body goes rigid, and the person loses consciousness and falls. The skin may turn bluish because the chest muscles are too stiff to breathe normally. This phase lasts roughly 10 to 20 seconds.
The Clonic Phase
The stiffness gives way to rhythmic jerking of the arms and legs, alternately flexing and relaxing. Breathing may be noisy or irregular. Saliva can build up or become frothy. The person may bite the side of their tongue (this happens in about 22% of seizures) or lose bladder control as the muscles relax between contractions. The clonic phase usually lasts one to two minutes, sometimes less.
The Recovery Phase
Once the jerking stops, the person enters what’s called the postictal state. This is not simply “waking up.” It typically lasts 5 to 30 minutes and involves deep confusion, drowsiness, headache, and nausea. Some people become agitated or emotional without understanding why. Bruises, scrapes, and soreness from the fall and muscle contractions are common. Back pain can occur if the force of the seizure compressed a vertebra.
Full recovery takes longer than most people expect. Confusion from a severe seizure can linger for hours, and in some cases up to one to two days. Some people experience temporary weakness on one side of the body afterward, which can take one to two days to resolve completely. Changes in mood, energy, and mental sharpness can persist for days.
Common Causes and Triggers
Epilepsy is the most common cause of recurring tonic-clonic seizures, but a person can have one without having epilepsy. Other causes include head injuries, brain infections, strokes, brain tumors, and severe electrolyte imbalances. In some cases, a first seizure has no identifiable cause.
For people who are prone to seizures, certain triggers make one more likely. Sleep deprivation is one of the most potent. Others include high fever, alcohol withdrawal, extreme stress, flashing lights (in photosensitive individuals), and missed doses of seizure medication. Knowing personal triggers is one of the most practical tools for reducing seizure frequency.
How Tonic-Clonic Seizures Are Diagnosed
After a first seizure, doctors typically start with a physical exam and an EEG, a test that records the electrical activity in your brain through sensors placed on the scalp. The EEG can reveal abnormal patterns that suggest epilepsy, even between seizures. An MRI of the brain is often the next step, because it produces detailed images that can identify structural problems like scarring, tumors, or evidence of a past stroke. In some situations, a CT scan is done first, especially in an emergency setting, because it’s faster and can quickly rule out bleeding or large abnormalities.
If infection or inflammation is suspected, a lumbar puncture (spinal tap) may be used to test cerebrospinal fluid. A more specialized test called magnetoencephalography measures magnetic fields produced by brain activity and helps pinpoint exactly where seizures originate. Not everyone needs every test. The workup depends on the circumstances of the seizure and your medical history.
What to Do If Someone Has a Seizure
If you witness a tonic-clonic seizure, the most important thing is to protect the person from injury without interfering with the seizure itself. Here’s what to do:
- Ease them to the ground if they’re falling, and clear away furniture, sharp objects, or anything nearby that could hurt them.
- Place something soft under their head, like a folded jacket.
- Roll them gently onto their side with the mouth pointing toward the ground. This keeps the airway clear and prevents choking on saliva.
- Remove eyeglasses and loosen anything tight around the neck.
- Time the seizure. If convulsions last longer than five minutes, call 911. Also call if the person doesn’t regain consciousness, has a second seizure, is injured, is pregnant, or has never had a seizure before.
Equally important is what not to do. Do not hold the person down or try to stop their movements, as this can cause injury to both of you. Do not put anything in their mouth. The old belief about swallowing the tongue is a myth, and forcing an object between clenched teeth can break teeth or injure the jaw. Do not attempt mouth-to-mouth breathing during the seizure; people almost always start breathing on their own once it ends. Do not offer food or water until the person is fully alert, because their swallowing reflex may not be reliable yet.
Long-Term Risks of Frequent Seizures
A single tonic-clonic seizure, while frightening, is not usually life-threatening. The more serious concern is recurrence. People who have frequent, uncontrolled tonic-clonic seizures face a higher risk of injuries from falls, including head trauma and compression fractures in the spine.
There is also a rare but serious risk called sudden unexpected death in epilepsy (SUDEP). Most cases occur during or shortly after a seizure, and the person is typically found in bed. The frequency of tonic-clonic seizures is the strongest known risk factor for SUDEP. This is one of the key reasons neurologists focus on reducing or eliminating tonic-clonic seizures specifically, even when other seizure types are also present. Effective seizure control through medication, lifestyle management, or in some cases surgery, significantly lowers this risk.