Tonic-Clonic Seizures

By: Nicholas Parekh

What is a seizure?

Seizures are neurological events characterized by sudden surges of electrical activity in the brain and are common in epileptic patients. Seizures usually last one to two minutes, and seizures that last for more than five minutes are considered to be a medical emergency. Patients are diagnosed with epilepsy when they have experienced two or more “unprovoked” seizures (i.e. seizures without a clear cause) that are more than 24 hours apart. “Provoked” seizures have non-epilepsy-related causes such as sleep deprivation or low blood sugar.

What is a tonic-clonic seizure?

When people think of seizures, they tend to think of the jerking and spasms associated with a tonic-clonic or grand-mal seizure. Despite the general public’s familiarity with them, tonic-clonic seizures are not very common, and most people who experience them only experience one in their lives.

Unlike partial (focal) seizures which affect an isolated area of the brain, generalized seizures affect the entire brain. Partial seizures can sometimes spread to the rest of the brain and transform into secondary generalized seizures. Tonic-clonic seizures are a subset of the more broad category of generalized seizures which also includes absence, atonic, and myoclonic seizures.

Under normal conditions, neurons are only actively firing in portions of the brain that are being used (e.g. areas of the brain involved in vision such as the occipital lobe are “on” when you are reading this article). However, during a tonic-clonic seizure, all parts of the brain are abnormally active and their neurons are firing simultaneously. This results in widespread effects such as the contraction of many different muscles at the same time and convulsion of the whole body.

Unlike individual tonic or clonic seizures, tonic-clonic seizures occur in 2 phases. First, the individual loses consciousness during the tonic phase. In this stage, their muscles rigidly contract for up to 20 seconds. “Tonic” refers to the increase in muscle tone caused by sustained muscle contraction during this phase. The rapid synchronized muscle contraction can result in the patient emitting a scream called an “epileptic cry” which is caused by the muscles surrounding the lungs contracting and forcing air through the contracted vocal cords.

The tonic phase is then followed by the clonic phase where the individual undergoes muscle spasms for several minutes. “Clonic” refers to the rhythmic cycles of muscle contraction and relaxation which are responsible for the jerking and muscle spasms associated with grand mal seizures.

The period following the seizure is known as the postictal state and can last for anywhere from minutes to days. Immediately after the seizure ends, an individual may return to some level of consciousness and experience disorientation and fear. These symptoms typically resolve within an hour. More concerning are other neurological symptoms like short-term memory loss and brain fog which can last for longer periods and impair one’s ability to carry out daily activities.

The underlying causes of the postictal state are not well understood. One theory is that affected areas of the brain have less blood flow and therefore less oxygen delivery following a seizure. This causes those parts of the brain to enter a state of hypoxia, or oxygen starvation, which would reduce brain function and contribute to issues like short-term memory loss and motor dysfunction. Another theory proposes that massive seizures like tonic-clonic seizures cause changes in neurotransmitter release, resulting in elevated levels of adenosine which can result in fatigue (caffeine blocks adenosine from binding to its receptors, making one feel less tired).


-loss of consciousness


-falling down

-body turning rigid

-involuntary urination or defecation

-feeling disoriented and fatigued after the event


-brain fog

-muscle soreness


A tonic-clonic seizure is relatively easy to identify due to the characteristic jerking and people’s familiarity with them. However, it is still important to consult with a physician after a major neurological event like a grand mal seizure. While the seizure itself may resolve on its own, a neurologist can help prevent future seizures by identifying the cause of the seizure and prescribing an appropriate course of treatment. Moreover, early and proactive treatment increases the likelihood of becoming seizure-free for patients with epilepsy.

A neurologist will first rule out non-epileptic causes of the seizure which could include electrolyte imbalances, low blood sugar, or sleep deprivation. If a specific cause of the seizure cannot be pinpointed and the patient is believed to have epilepsy, they may undergo an electroencephalogram (EEG) to record the electrical activity of the brain and spot abnormal brain wave patterns associated with epilepsy. Magnetic resonance imaging (MRI) or computed tomography (CT) scans may also be used to visualize the structure of the brain and look for scarring, malformations, or tumors.


When the cause of the seizure can be identified and is non-epileptic, treatment usually directly addresses the issue (e.g. getting more sleep). If the patient has epilepsy, then they are usually treated with anti-epileptic drugs like Depakote and Keppra which prevent seizures from occurring.


Harvard Health Publishing. “Generalized Seizures (Grand Mal Seizures).” Harvard Health, Harvard Health Publishing, Apr. 2019,

International League Against Epilepsy. “After the Wave Subsides: Post-Ictal Effects.” International League Against Epilepsy, International League Against Epilepsy, 2020,

Johns Hopkins Medicine. “Generalized Seizures.” Johns Hopkins Medicine, Accessed 18 Feb. 2021.

Mayo Clinic. “Grand Mal Seizure – Symptoms and Causes.” Mayo Clinic, Mayo Clinic, 18 June 2019,

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