Tonic seizures cause sudden stiffness and rigidity in your muscles. They typically last less than 1 minute.

Seizures are rapid bursts of electrical activity in your brain that can cause involuntary movement and a loss of awareness or consciousness. There are different classifications of seizures. These depend on factors like the part of your brain that’s affected and the symptoms the seizure causes.

Tonic seizures are characterized by sudden muscle stiffness in your limbs or torso. They can occur when you’re awake or asleep and usually last less than a minute.

Anyone can have a seizure, but most people with recurrent seizures have a neurological condition known as epilepsy. Epilepsy exists on a spectrum. This means the type, frequency, and severity of seizures varies considerably between individuals.

About 11% of people in the United States experience a seizure in their lifetime.

Read on to learn more about tonic seizures, including what causes them and how they differ from other types of seizures.

What are tonic seizures?

Your nervous system (which includes your brain) uses electrical impulses to send and receive messages throughout your body. Seizures are abnormal bursts of electrical activity that interfere with this system, causing disruptions that can lead to many different symptoms.

Tonic seizures cause sudden, temporary stiffness in your limbs and trunk. The name “tonic” comes from “muscle tone.” Your muscle tone is the stiffness of your muscles at rest.

During a tonic seizure, your muscles become stiff and rigid. If you’re standing, you may fall to the floor. These seizures are often brief and tend to occur during sleep.

Tonic seizures can be focal or generalized.

  • Focal seizures: These are caused by abnormal electrical activity that starts in one region of your brain.
  • Generalized seizures: These are caused by abnormal electrical activity in both sides of your brain.
  • Focal tonic seizures: These cause symptoms in one part of your body.
  • Generalized tonic seizures: These cause symptoms throughout your body.

Focal tonic seizures can spread and become generalized. When this happens, they’re called focal to bilateral tonic seizures.

Tonic vs. tonic-clonic seizure

Tonic-clonic seizures used to be called grand mal seizures. They’re the type of seizure many people think of when they think of epilepsy. A tonic-clonic seizure shares features of both tonic and clonic seizures.

Tonic-clonic seizures start with the tonic phase, where your muscles suddenly stiffen and twitch. It then enters the clonic stage, where you might lose consciousness or awareness of your surroundings.

Symptoms of seizures Tonic Clonic Tonic-clonic
Muscle stiffness yes no yes
Muscle twitching and jerking no yes yes
Awareness normal or slightly altered consciousness normal or slightly altered consciousness loss of consciousness

What does a tonic seizure look like?

If you witness someone having a tonic seizure, you may notice their arms or legs become stiff as a board. Their upper body may also straighten and become rigid. If they’re standing, they may fall to the floor and continue to appear stiff in one or more areas of their body.

Tonic seizures are generally brief. In a 2023 study, researchers found that 95% of generalized tonic seizures lasted 3 to 36 seconds. They also found that 95% of focal tonic seizures lasted 2 to 148 seconds.

Half of generalized tonic seizures lasted less than 8.5 seconds and half of focal tonic seizures lasted less than 16.5 seconds.

How to help someone having a tonic seizure

Most seizures don’t require emergency medical attention. According to the Centers for Disease Control and Prevention (CDC), the best way to help somebody having any type of seizure is:

  • Stay with them until they’re fully awake.
  • Comfort them and speak calmly.
  • Check to see if they have a medical bracelet with emergency information.
  • Keep yourself and other people around you calm.
  • Help them sit in a safe place when the seizure is over and explain what happened.
  • Offer to help the person get home.

What happens after a tonic seizure?

The period after a seizure is called the postictal phase. It typically lasts between 5 and 30 minutes. During this phase, the person may:

  • be confused
  • be drowsy
  • have high blood pressure
  • have a headache
  • be nauseous

Most of the time, it’s not necessary to get medical attention. But it’s important to call 911 or local emergency services if somebody you’re with:

  • has a seizure that lasts longer than 5 minutes
  • doesn’t regain full consciousness
  • has their first seizure
  • has another seizure after their first one
  • has trouble breathing or walking after their seizure
  • has a seizure in water
  • has an underlying health condition such as pregnancy, heart disease, or diabetes

What causes tonic seizures?

Like other types of seizures, tonic seizures are caused by abnormal surges of electrical information in your brain. There are many potential causes of seizures. Focal tonic seizures are associated with the activation of a part of your brain called Brodmann area 6.

Tonic seizures are often seen in people who experienced hypoxic ischemic encephalopathy around birth. Hypoxic ischemic brain injuries happen because of a lack of oxygen in your brain.

It can also happen in people with intraventricular hemorrhage. Intraventricular hemorrhage is bleeding in the spaces that allow fluid to flow out of your brain.

According to the Epilepsy Foundation, tonic seizures are common among people who have Lennox-Gastaut syndrome and other types of epilepsy.

Lennox-Gastaut syndrome is a severe type of epilepsy that usually develops before 4 years of age. It can be caused by:

  • brain malfunctions
  • tuberous sclerosis
  • lack of oxygen around birth (perinatal asphyxia)
  • severe head injury
  • brain infection
  • genetic conditions

In a 2019 case study, researchers reported tonic seizures associated with autoimmune epilepsy.


How are seizure disorders diagnosed?

Seizure disorders are usually diagnosed by a type of specialist called a neurologist.

Bring a written description of what happens during your seizures. Or have someone take a video and bring that along for the doctor to review. This is an important part of the diagnosis process. A neurologist can use this information to narrow down which type of seizure you’re having.

A neurologist can run various tests to help find the underlying cause of your seizures. They’ll likely give you a test called an electroencephalogram (EEG). This test uses special sensors placed on your head to detect any unusual electrical activity in your brain.

A doctor may also recommend a brain scan to look for brain tumors or structural abnormalities in your brain.

Blood tests can help a doctor rule out genetic conditions or signs of infection.


How are tonic seizures treated?

The most common treatment for seizures is antiseizure medications. These drugs help control seizures in about 70% of people with epilepsy.

Many different types of medications are used to control seizures. You may need to try several different combinations of medications before finding one that’s effective.

Other treatments for seizures can include:

  • vagus nerve stimulation
  • deep brain stimulation
  • dietary changes such as following a ketogenic diet
  • surgery


Tonic seizures are brief periods of sudden muscle stiffness caused by electrical changes in your brain. They usually last less than a minute and are associated with Lennox-Gastaut syndrome and some other epileptic syndromes.

Tonic seizures are often controllable with medications. You may have to take several types of medication before finding one that successfully controls your seizures.


Source:, Daniel Yetman, Nancy Hammmond, MD