Our brain cells send signals to one another constantly – these signals allow us to think, feel, and function. Typically, the signals are delicately balanced to ensure there is not too much (or too little) activity. But what happens when those signals are disrupted, or acting abnormally?

On this page, we’ll explore seizures: what they are, what causes them, and how they relate to epilepsy.


A seizure is an electrical disturbance in the brain that interferes with its normal function. Many scientists and clinicians compare it to an “electrical storm in the brain” in which your brain cells hyper-synchronize in an abnormal pattern, disrupting that delicate brain signal balance.

Seizures vary from person-to-person, depending upon their seizure type. That’s because epilepsy is a spectrum disorder, meaning the causes, type, and severity can differ greatly amongst those affected by it. Some people have visible symptoms, such as a tonic-clonic seizure (previously called grand-mal), and others may have no visible symptoms, such as absence seizures (previously called petit mal).


In the words of Dr. Robert S. Fisher, “a seizure is the event…whereas epilepsy is the condition of seizures that spontaneously come back on their own.” Therefore, it’s possible to experience a seizure (such as a febrile seizure) and not have epilepsy. A person is considered to have epilepsy if they have two or more unprovoked seizures more than 24-hours apart, or if they have one seizure with a probability of having future seizures.

Learn more about epilepsy  »


The underlying causes of seizures are complex. Seizures can develop from a range of events, from faulty wiring during brain development to brain inflammation, or from physical injuries to infections. Unfortunately, in 50% of cases, the cause is unknown.

Certain events or situations may increase the likelihood of a seizure occurring in people with epilepsy; these are called seizure triggers. Some common triggers include:

  • Use of alcohol or drugs
  • Flashing lights
  • Stress
  • Not getting enough sleep
  • Certain types of foods, caffeine
  • Changes in blood sugar
  • Common cold, flu, or other illness
  • Menstruation
  • Not taking medication

Triggers vary from person to person, and an individual may have multiple triggers.

The causes of seizures by age


When identifying seizure types, they are first grouped into one of two broad categories – focal onset and generalized onset – based on where they start in the brain.

Your brain has two hemispheres, or halves: the left hemisphere and the right hemisphere. The hemispheres are separated by a fissure – a deep groove. The sides can communicate with each other because they are connected by the corpus callosum, a large bundle of nerve fibers. Focal seizures start on and only involve one hemisphere of the brain. Generalized seizures, on the other hand, involve both hemispheres. Sometimes, the onset (where the seizure starts) may be unknown.3

It is possible for a seizure to start on one side of the brain and then spread to the other side. When this happens, it is referred to as a focal to bilateral seizure.

The types of Seizures

Next, seizures are classified by looking at additional features, such as whether the seizure impairs your consciousness and what type of movements, if any, are involved. The combination of seizure onset and seizure features determine the type of seizure a person has experienced.

Learn more about the types of seizures  »


The signs and symptoms of a seizure will vary from person to person, as well as the type, severity, and phase of the seizure. General signs and symptoms can include:

  • Unusual behaviors/sensations
  • Uncontrollable movements
  • Loss of consciousness

It’s important to remember that some seizures are visible to others, whereas others are not. Most seizures last between 30 seconds and 2 minutes; if a seizure lasts longer than 5 minutes, you should seek medical care immediately.



  1. Sirven JI. Epilepsy: A Spectrum Disorder Cold Spring Harb Perspect Med. 2015 Sep 1;5:a022848.
  2. Simon D. Shorvon FA, Renzo Guerrini. The Causes of Epilepsy: Common and Uncommon Causes in Adults and Children: Cambridge University Press; 2011.
  3. Fisher RS, Cross JH, D’Souza C, French JA, Haut SR, Higurashi N, et al. Instruction manual for the ILAE 2017 operational classification of seizure types Epilepsia. 2017 Apr;58:531-542.

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