Fainting, or syncope, is a sudden and temporary loss of consciousness. This usually occurs due to a lack of oxygen reaching the brain.

Many things can cause oxygen deprivation to the brain, including low blood pressure.

Fainting is not usually serious. However, sometimes it can indicate a serious medical issue. People should treat every case of fainting as a medical emergency until they have uncovered the cause and treated the symptoms.

In this article, we look at why fainting occurs and when to seek medical treatment.

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Fainting is the body’s way of preserving oxygen in the brain.

Fainting usually results from a lack of oxygen to the brain, such as from problems with the lungs or blood circulation or carbon monoxide poisoning.

Fainting is a survival mechanism. If blood and oxygen levels in the brain drop too low, the body immediately starts shutting down nonvital parts to direct resources to vital organs.

When the brain detects lower levels of oxygen, breathing will speed up to increase the levels.

The heart rate will also increase, so that more oxygen reaches the brain. This reduces blood pressure in other parts of the body. The brain then receives extra blood at the expense of other body areas.

Hyperventilation plus hypotension may result in short term loss of consciousness, muscle weakening, and fainting.

Different underlying causes can cause a person to faint. We discuss some of them in detail below:

Neurocardiogenic syncope

Neurocardiogenic syncope develops due to a short term malfunction of the autonomous nervous system (ANS). Some people call it neurally mediated syncope (NMS).

The ANS controls automatic body functions, including heart rate, digestion, and respiration rate.

In NMS, a drop in blood pressure slows the heartbeat and pulse rate. This temporarily interrupts the brain’s blood and oxygen supply.

Possible triggers of neurocardiogenic syncope include:

  • an unpleasant or shocking image, such as seeing blood
  • sudden exposure to an unpleasant sight or experience
  • abrupt emotional upset, such as after receiving tragic news
  • extreme embarrassment
  • standing still for a long time
  • being in a hot and stuffy environment for a long time

Occupational syncope

Occupation, or situational, syncope is a type of neurocardiogenic syncope with physical rather than emotional, mental, or abstract triggers. Triggers include:

  • laughing or swallowing
  • passing stools or urine
  • coughing or sneezing
  • strenuous physical activities, such as lifting a heavy weight

Orthostatic hypotension

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Excessive alcohol consumption may increase the risk of fainting.

Orthostatic hypotension refers to fainting after standing up too quickly from a seated or horizontal position.

Gravity pulls blood into the legs, bringing down blood pressure elsewhere in the body. The nervous system usually reacts to this by increasing the heartbeat and narrowing the blood vessels. This stabilizes blood pressure.

However, if something undermines this stabilization process, there may be poor blood and oxygen supply to the brain, leading to fainting.

Triggers include:

Dehydration: If body fluid levels drop, so will blood pressure. This can make it harder for the blood pressure to stabilize. Therefore, less blood and oxygen reaches the brain.

Uncontrolled diabetes: A person with diabetes may need to urinate frequently, leading to dehydration. High blood sugar levels can damage certain nerves, especially those that regulate blood pressure.

Some medications: Taking diuretics, beta-blockers, and antihypertensive drugs may cause orthostatic hypotension in some people.

Alcohol: Some people faint if they consume too much alcohol in a short amount of time.

Some neurological conditions: Parkinson’s disease and other neurological conditions affect the nervous system. This may lead to orthostatic hypotension.

Carotid sinus syndrome: The carotid artery is the main artery that supplies blood to the brain. When there is pressure on the pressure sensors, or carotid sinus, in the carotid artery, it can cause fainting.

If a person’s carotid sinus is very sensitive, blood pressure may drop when they turn the head to one side, wear a tight collar or tie, or move over the carotid sinus while shaving. This may result in fainting.

This is more common among older males.

Cardiac syncope

An underlying heart problem may reduce blood and oxygen supply to the brain.

Possible heart conditions include:

This cause of fainting usually requires immediate medical treatment and extensive monitoring.

Apart from distinguishing episodes of fainting by their underlying cause, one of two different types of fainting might occur:

  • Pre- or near-syncope: This occurs when a person can remember events or sensations during the loss of consciousness, such as dizziness, blurred vision, and muscle weakness. They may remember falling before hitting their head and losing consciousness.
  • Syncope: This occurs when a person can remember the feelings of dizziness and loss of vision but not the fall itself.

Losing consciousness is the primary symptom of fainting. The following symptoms may occur leading up to a fainting episode:

  • a feeling of heaviness in the legs
  • blurred or “tunnel” vision
  • confusion
  • feeling warm or hot
  • lightheadedness, dizziness, or a floating feeling
  • nausea
  • sweating
  • vomiting
  • yawning

When a person faints, they may:

  • fall over or slump
  • appear unusually pale
  • have reduced blood pressure and a weak pulse

If a person with an underlying health condition faints, they will require treatment. This will help prevent future fainting episodes. Often, however, no further treatment is necessary.

To help prevent further fainting episodes, people should try to avoid triggers, such as long periods of standing still, dehydration, and spending a lot of time in hot environments.

If the sight or thought of injections or blood make a person feel faint, they should tell their doctor or nurse before undergoing a medical procedure that may involve this. The doctor or nurse can then make sure that the individual is in a safe position, such as lying down, before starting the procedure.

People mainly use beta-blockers to treat high blood pressure. However, these drugs may also help if neurocardiogenic syncope interferes with a person’s quality of life.

However, some adverse effects of beta-blockers include fatigue, cold hands and feet, a slow heartbeat and pulse, nausea, and diarrhea.

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If someone faints, lie them on their back and try to loosen restrictive clothing.

People who feel themselves becoming faint should do the following:

  • Find a safe place to sit or lie down.
  • When sitting, place their head between their knees.
  • When standing up again, do so slowly.

If a person notices that somebody is fainting or about to faint, they can intervene in the following ways:

  • Lie the individual down on their back.
  • If they are breathing, raise their legs about 12 inches above heart level to restore blood flow to the brain.
  • Try to loosen all belts, ties, collars, and other forms of restrictive clothing.
  • When the person regains consciousness, do not let them get up too quickly.
  • If they remain unconscious for more than about a minute, put them in the recovery position and get emergency medical help.

If the person is not breathing:

  • Check for breathing, coughing, or movement.
  • Make sure that the airway is clear.
  • If there is no sign of breathing or circulation, start cardiopulmonary resuscitation (CPR).
  • Continue CPR until either help arrives or the person starts breathing on their own.
  • Put them in the recovery position and stay with them until help comes.
  • If the individual is bleeding after the fall, apply direct pressure to the wound to help control the bleeding.

Here, learn more about how to perform CPR.

A fainting episode may be the symptom of a more severe underlying condition, such as stroke.

If the person experiences numbness in the face, paralysis, weakness, numbness in one arm, or slurred speech, they need emergency medical help.

People should seek medical assistance if:

  • they experienced chest pains or an irregular, pounding heartbeat before losing consciousness
  • they have a history of heart disease
  • fainting caused an injury
  • fecal or urinary incontinence occurred before fainting
  • they have fainted while pregnant
  • they experience recurring episodes of fainting
  • they also have diabetes
  • they were unconscious for more than a few minutes after fainting

The doctor will need to know about:

  • the person’s medical history and any medications they take regularly
  • whether the person faints often, and if so, details of previous episodes
  • whether or not the person has a family history of heart disease
  • what the person was doing and where they were just before fainting occurred
  • any other co-occurring symptoms

The doctor will listen to the heart to check for underlying cardiac conditions. If they suspect a heart problem, the person may need to see a heart specialist, or a cardiologist.

Tests may include:

  • an electrocardiogram, to check the electrical activity of the heart
  • carotid sinus stimulation, to determine whether this triggers lightheadedness or dizziness
  • blood tests, to check for anemia, diabetes, or an infection
  • tilt-table test, to monitor blood pressure, heart rhythm, and heart rate while the person moves from lying down to an upright position
  • a Holter monitor test, in which an individual wears a portable device under their clothing that monitors every heartbeat for 1–2 days

A person can press a button on the Holter monitor if they feel as though they are about to faint. Records will display the heart rhythms that were present at that moment.

If none of these tests reveal any unusual activity, the doctor will conclude that the person experienced neurocardiogenic syncope. They will not recommend any treatment in these circumstances.