A tonic-clonic seizure, previously known as a grand mal seizure, causes a loss of consciousness and violent muscle contractions. It's the type of seizure most people picture when they think about seizures.

During a seizure, there's a burst of electrical activity in the brain that causes changes in behavior and movements. Seizures can be focal, meaning the burst of electrical activity happens in one area of the brain. Or seizures can be generalized, in which they result in electrical activity in all areas of the brain. Tonic-clonic seizures may begin as focal seizures in a small area of the brain and spread to become generalized seizures that involve the whole brain.

Focal and generalized seizures have different symptoms. People who have generalized seizures usually lose consciousness. But people who have focal seizures may or may not lose consciousness. In tonic-clonic seizures, the muscles become stiff, causing the person to fall. Then the muscles alternately flex and relax.

Usually, a tonic-clonic seizure is caused by epilepsy. But sometimes this type of seizure can be triggered by other health problems. Very low blood sugar, a high fever or a stroke can cause a tonic-conic seizure.

Many people who have a tonic-clonic seizure never have another one and don't need treatment. But someone who has recurrent seizures may need treatment with daily anti-seizure medicines to control and prevent future tonic-clonic seizures.


Tonic-clonic seizures have two stages:

  • Tonic phase. Loss of consciousness occurs. The muscles suddenly contract and cause the person to fall down. This phase tends to last about 10 to 20 seconds.
  • Clonic phase. The muscles go into rhythmic contractions. They alternately flex and relax. Convulsions usually last 1 to 2 minutes or less.

The following symptoms occur in some but not all people with tonic-clonic seizures:

  • A scream. Some people may cry out at the beginning of a seizure.
  • Loss of bowel and bladder control. This may happen during or following a seizure.
  • Not responding after convulsions. The person may not become conscious for several minutes after convulsions have ended.
  • Confusion. The person often is disoriented after a tonic-clonic seizure. This is referred to as postictal confusion.
  • Fatigue. Sleepiness is common after a tonic-clonic seizure.
  • Bad headache. Headaches may occur after a tonic-clonic seizure.

When to see a doctor

Call 911 or emergency medical help if:

  • The seizure lasts more than five minutes.
  • Breathing or consciousness doesn't return after the seizure stops.
  • A second seizure follows immediately.
  • You have a high fever.
  • You're experiencing heat exhaustion.
  • You're pregnant.
  • You have diabetes.
  • You've injured yourself during the seizure.

If you experience a seizure for the first time, see a healthcare professional.

Also see a healthcare professional if you or your child:

  • Experience an increasing number of seizures for no apparent reason.
  • Notice new seizure symptoms.


The brain's nerve cells typically communicate by sending electrical and chemical signals across the synapses that connect the cells. Tonic-clonic seizures occur when there's a surge of electrical activity over the surface of the brain. Many nerve cells fire at once, much faster than usual. Exactly what causes the changes to occur often is not known.

However, tonic-clonic seizures are sometimes caused by underlying health problems, such as:

Injury or infection

  • Traumatic head injuries.
  • Infections, such as encephalitis or meningitis. Or a history of such infections.
  • Injury due to a previous lack of oxygen.
  • Stroke.

Congenital or developmental factors

  • Blood vessels that don't form properly in the brain.
  • Genetic syndromes.
  • Brain tumors.

Metabolic issues

  • Very low blood levels of glucose, sodium, calcium or magnesium.

Withdrawal syndromes

  • Using or withdrawing from drugs, including alcohol.

Risk factors

Risk factors for tonic-clonic seizures include:

  • A family history of seizure disorders.
  • Any injury to the brain from trauma, a stroke, previous infection and other causes.
  • Sleep deprivation.
  • Medical problems that affect electrolyte balance.
  • Illicit drug use.
  • Heavy alcohol use.


Having a seizure at certain times can be dangerous for you or others. You might be at risk of:

  • Falling. If you fall during a seizure, you can injure your head or break a bone.
  • Drowning. If you have a seizure while swimming or bathing, you're at risk of accidental drowning.
  • Car accidents. A seizure that causes either loss of awareness or control can be dangerous if you're driving a car or operating other equipment.
  • Pregnancy complications. Seizures during pregnancy pose dangers to both mother and baby. And certain anti-seizure medicines increase the risk of birth defects. If you have epilepsy and plan to become pregnant, talk with a healthcare professional. Your medicines may need to be adjusted. A healthcare professional likely will monitor your pregnancy.
  • Emotional health issues. People with seizures are more likely to have depression and anxiety. Emotional health issues may be a result of dealing with the condition itself or as a result of medicine side effects.

Dec. 12, 2023
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