Syncope and seizures can both cause a loss of consciousness. However, seizures often involve convulsions, which are unusual in syncope or fainting.

Seizures and syncope share similar symptoms and can both have serious causes. However, around halfTrusted Source of syncope cases are due to a fall in blood pressure.

Anyone who experiences syncope or seizure needs to consult a doctor.

This article compares syncope and seizures. It provides an overview of the conditions and their causes and symptoms. It also outlines how to respond to seizures and syncope and how doctors diagnose them.

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SyncopeSeizures
defining symptom is loss of consciousnesscommon symptoms include convulsions
less likely to cause tongue bitingmore likely to cause tongue biting
less likely to show an atypical electroencephalogram (EEG) readingmore likely to show a specific atypical EEG reading
often arises due to a drop in blood pressurecan arise from different conditions that alter typical brain activity, including epilepsy
could indicate reduced blood flow in the braincould indicate stroke, cancer, or brain infections
does not arise from atypical brain activitydoes arise from atypical brain activity
may not require urgent medical attention if there are no lasting symptomsoften requires urgent medical attention

A 2022 reviewTrusted Source defines syncope as a temporary loss of consciousness. The affected individual will also be unable to hold themselves upright. A person recovers from syncope on their own. People refer to syncope as “passing out” or “fainting.”

Causes

There are many possible causes of syncope, ranging from harmless to life threatening. These conditions include:

Around 50%Trusted Source of all syncope is due to a fall in blood pressure. Doctors call this vasovagal syncope, or the “common faint.” It can arise for many different reasons, such as:

  • stress
  • fatigue
  • prolonged standing
  • being in a crowded place
  • being in a hot environment

Common faints can also occur in people with no underlying health problems.

Symptoms

Several symptoms can precedeTrusted Source a common faint. These include:

An individual will also have an atypically slow heart rate, below 60 beats per minuteTrusted Source. However, they may not notice this sign of vasovagal syncope.

What to do if someone faints

The United Kingdom’s National Health Service (NHS) provides guidance on what to do if someone faints.

If an individual believes they experienced fainting, they need to discuss it with a doctor. A doctor will ask questions about the person’s symptoms before the episode, which will help them determine the cause.

If an individual sees someone faint, they need to try to remain calm before waiting for the person to wake up. The individual needs to lay them on their back, with their legs raised if possible. However, it is better to lay a pregnant person on their side.

An individual needs to contact the emergency services if someone passes out and any of the following occurs:

  • they do not wake after 1 minute
  • they are not breathing
  • they find it hard to move or speak
  • they have chest pain or heart palpitations
  • they have injured themselves
  • they have fainted while exercising or lying down

An individual should also contact the emergency services if the person is shaking or jerking.

What is convulsive syncope?

According to an older article, convulsive syncope is not a form of seizure. Rather, convulsive syncope is when someone’s muscles briefly shake or jerk while the individual is unconscious. This can occur when there is reduced blood flow to the brain.

A convulsive syncope is not the same as a syncope-induced seizure. These are “anoxic-epileptic” seizures.

According to a 2023 reviewTrusted Source, seizures are uncontrolled periods of atypical brain activity. These can cause various changes in consciousness, memory, feeling, or behavior. Seizures can affect different parts of the brain.

Causes

There are many possible causes of seizures. When a seizure has a cause, doctors call it “provoked.” Causes of a provoked seizure include:

If someone experiences two or more unprovoked seizures, doctors may diagnose epilepsy. Epilepsy may arise from a genetic susceptibility or damage to the brain.

Symptoms

Seizures can cause various symptoms, and a loss of consciousness and convulsions are commonTrusted Source. For some seizure types, convulsions usually start with stiffening muscles. The convulsions then enter a phase of rhythmic movement.

Seizures can cause various symptoms, including a loss of consciousness and convulsions. For some seizure types, convulsions usually start with stiffening muscles. The convulsions then enter a phase of rhythmic movement.

An individual may also:

  • cry out or make a noise when the seizure starts
  • bite their tongue
  • have urinary incontinence

Some people report a strange feeling before the seizure. Doctors sometimes call this an “aura.”

What to do

The Epilepsy Foundation gives advice for seizure first aid. It is important to call the emergency services when:

  • it is a person’s first seizure
  • repeated seizures happen one after another
  • the person appears to be choking or having difficulty breathing
  • the seizure happens in water
  • it lasts more than 5 minutes
  • the person is injured

According to a 2022 paperTrusted Source, doctors have ways of differentiating between seizures and syncope.

Doctors may or may not be able to gather information about an individual’s symptoms and behavior before the episode — either from the individual or people nearby at the time. However, syncope can cause similar symptoms to a seizure, such as convulsions and tongue-biting. So, an overview of symptoms is not always enough to make a diagnosis.

Doctors can also use an EEG, which measures brain activity. This can help detect the sorts of brain activity that characterizes seizures.

In the future, testing for levels of certain chemicals may also help with diagnosis. A small 2022 studyTrusted Source involving 111 people in Iran noted that seizures lead to significantly higher levels of certain biomarkers in comparison with syncope. Those biomarkers are:

  • neuron-specific enolase
  • creatine phosphokinase
  • serum lactate dehydrogenase

The study authors suggest that testing for these biomarkers may be useful to confirm a seizure diagnosis.

Anyone who notices someone having a seizure or fainting needs to contact emergency services. Aside from possible serious causes, individuals can hurt themselves when falling and require medical attention.

An individual who has experienced one or more seizures or episodes of passing out needs to seek a doctor’s advice.

Syncope is a temporary loss of consciousness and inability to hold oneself upright. The causes of syncope include cardiac arrhythmias, reduced blood flow to the back of the brain, and low blood pressure. The latter can arise from fatigue, stress, or being in a crowded place.

Seizures involve uncontrolled and atypical brain activity. Epilepsy is a disorder of the brain that causes repeated seizures. Doctors diagnose epilepsy when a person experiences two or more seizures.

Seizures can have many causes, such as electrolyte imbalances, drug withdrawal, and fever. Seizures can also be due to life threatening conditions, including brain infections, brain injury, and stroke.

People who experience syncope or a seizure can discuss the episode with a doctor who will try to determine the cause.