Fainting

Page last reviewed: 13/07/2011

Fainting is a sudden, temporary loss of consciousness that usually results in a fall. Healthcare professionals often use the term 'syncope' when referring to fainting because it distinguishes fainting from other causes of temporary unconsciousness, such as seizures (fits) or concussion. 

Why fainting happens

In order to function properly, the brain relies on oxygen that is carried in the blood. Fainting can occur when the blood flow to the brain is reduced. This is usually brief and quickly corrected by the body, but it can cause people to feel odd, sweaty and dizzy. If it lasts long enough, they may fall down. This is called a faint.

The cause of the reduced blood supply to the brain can vary, but it is sometimes caused by blood pooling in the big veins in the legs. When someone stands up, it is more difficult to get blood back to the heart, which means there is less blood to pump to the brain. Most people faint from standing, although occasionally fainting can occur from sitting.

When someone falls down, the blood flows more easily from the legs back to the heart and then on to the brain. As their brain receives more blood, they recover from the faint. 

Other factors that can make fainting more likely include:

  • reduced blood volume, for example, if someone has not drunk enough water
  • anything that slows the heart down, for example, being sick

See Fainting - causes for more information.

How common is fainting?

Fainting is very common. About 1 young child in 100 may faint, for example, as a result of a fear or pain. One study found that, by 40 years of age, 95 out of 100 people had fainted at least once.

Studies across Europe suggest that about 1 visit in 100 to the emergency departments of hospitals are due to fainting. Fainting becomes more common with age.

Outlook

Around a third of people who have fainted may faint again within three years. In general, the more someone faints, the more likely they are to faint again.

People who faint are at considerable risk of injury when they fall to the ground. Nearly a third of people experience minor bruises or cuts after a fall. Less commonly, people may fracture a bone or the faint could cause a car accident.  

It is important that a healthcare professional investigates the cause of a fainting episode to rule out heart conditions (see Fainting - diagnosis). Treatment for fainting involves:

  • avoiding the triggers of fainting, for example, avoiding hot and crowded environments
  • being prepared to deal with fainting, for example, spotting the warning signs of fainting, such as feeling lightheaded, and lying down to increase blood flow to the brain

See Fainting - treatment for more information about what to do if someone is about to faint or has fainted. 

Concussion
Mild, reversible brain damage, which can last a few seconds or a few hours, usually after a head injury.

Veins
Veins are a type of blood vessel. They carry blood back to the heart.

Page last reviewed: 13/07/2011

When you faint, you will feel weak and unsteady before passing out for a short period of time, usually only a few seconds. Fainting can happen when you are sitting down, standing up or when you get up too quickly.

Warning symptoms

Just before losing consciousness, you may experience the following symptoms:

  • yawning
  • a sudden, clammy sweat
  • nausea (feeling sick)
  • fast, deep breathing
  • confusion
  • feeling lightheaded
  • blurred vision or spots in front of your eyes
  • ringing in your ears

This is followed by a loss of strength and a loss of consciousness. It only takes a few seconds to run through these symptoms, and there may be very little warning before you collapse. In some cases, there may be no other symptoms to warn you that you are about to faint.

When you collapse to the ground, your head and heart are on the same level. This means that your heart does not have to work as hard to push blood up to your brain. You should return to consciousness after about 20 seconds. In rare cases, you may remain unconscious for longer, perhaps several minutes.

Afterwards

After fainting, you may feel confused and weak for about 20 to 30 minutes. You may also feel tired. Sometimes, older people may not be able to remember what they were doing just before they fainted.

Page last reviewed: 13/07/2011

Fainting (syncope) is a defence mechanism used by the brain. If the supply of blood and oxygen to the brain becomes too low, the brain will immediately take any available blood and oxygen from the rest of the body at the expense of other bodily functions.

Your breathing rate will be increased (hyperventilation) as your brain tries to increase its supply of oxygen. Your heart rate will also increase, to pump more blood from the rest of your body to your brain.

The increase in heart rate will lead to a loss of blood pressure in the rest of your body (hypotension) as blood is diverted to your brain. The combination of hyperventilation and hypotension can then lead to a temporary loss of consciousness and muscle weakness, resulting in fainting.

There are different types of fainting which are caused by the blood supply to the brain being interrupted for different reasons. The different types of fainting are explained below.

Neurally mediated syncope

Neurally mediated syncope is also called reflex syncope. Neurally means that it is related to the nervous system, which is made up of your brain, nerves and spinal cord. There are three types of neurally mediated syncope. They are:

  • vasovagal syncope
  • situational syncope
  • carotid sinus syndrome

These are explained in more detail below.

Vasovagal syncope

Vasovagal syncope occurs when something triggers a temporary malfunction in your autonomic nervous system. The autonomic nervous system is the part of the nervous system responsible for regulating many of the body's automatic functions, such as heartbeat and blood pressure.

The malfunction in the autonomic nervous system causes a drop in your blood pressure and a reduction in your heartbeat. This leads to a temporary interruption to your brain's blood supply.

Vasovagal syncope may be caused by:

  • sudden exposure to an unpleasant sight or experience, such as the sight of blood
  • standing for long periods of time
  • spending a long time in hot or stuffy environments
  • a sudden intense episode of stress, emotional upset, fear or anxiety
  • a sudden feeling of pain

Situational syncope

Situational syncope is also a type of fainting related to the nervous system. It occurs when a bodily function or activity places a sudden strain on your autonomic nervous system. Possible causes of situational syncope include:

  • coughing
  • sneezing
  • swallowing
  • laughing
  • passing stools
  • urinating
  • some physical activities, such as weightlifting, although this could also be a sign of an underlying heart problem (see cardiac syncope, below)

Situational syncope may also occur after eating a meal or exercising.

Carotid sinus syndrome

The carotid sinus is a collection of sensors in the carotid artery. The carotid artery is located in your neck and is the main artery that supplies blood to your brain. The carotid sinus helps to regulate the flow of blood through the carotid artery into your brain.

Some people can develop a hypersensitive carotid sinus. This means that any physical stimulation of the carotid sinus can cause the sensors suddenly to trigger a drop in blood pressure, resulting in fainting. This condition is known as carotid sinus syndrome.

Examples of physical stimulation that may affect your carotid sinus include:

  • turning your head to one side
  • wearing a tight collar
  • shaving over the part of your neck that contains the carotid sinus

Carotid sinus syndrome is very rare in people who are under 40 years of age. It is most common among older men.

Orthostatic hypotension

Orthostatic hypotension is a condition in which your blood pressure falls suddenly when you stand up, which can cause fainting. It is more common in older people, and is the reason for fainting in 1 person in 10 aged 60 years or over who faint.

When you stand up after sitting or lying down, gravity naturally draws your blood down into your legs, reducing your blood pressure. Usually, the nervous system counteracts this effect by making your heart beat faster and narrowing your blood vessels, both of which will stabilise your blood pressure.

However, in cases of orthostatic hypotension, something interrupts the process of stabilisation. This means that if you stand up suddenly, the blood supply to your brain is interrupted, causing you to faint.

Some possible causes of orthostatic hypotension are explained below. 

  • Dehydration (low blood volume). If you become severely dehydrated (where the normal water content of your body is reduced), the amount of fluid in your blood will reduce along with your blood pressure. This will make it much harder for your nervous system to stabilise your blood pressure, increasing your chances of fainting. This can be caused by heavy bleeding, vomiting or diarrhoea.
  • Diabetes - untreated diabetes (a condition where there is too much glucose in the blood) causes frequent urination, which can lead to dehydration. Excess glucose in the blood can also damage the nerves that help to regulate your blood pressure.
  • Medication. Some medicines can cause orthostatic hypotension in some people. These include diuretics, which increase the production and flow of urine from the body, beta - blockers and some types of antidepressants.
  • Neurological conditions. Some health conditions that affect the nervous system, such as Parkinson's disease, can trigger orthostatic hypotension in some people.

Cardiac syncope

Cardiac syncope is where the blood supply to the brain is interrupted due to an underlying problem with your heart. Possible causes of cardiac syncope include:

  • abnormal heart rhythms (arrhythmias)
  • narrowing of the heart valves (stenosis)
  • heart attack, which is a medical emergency when the blood supply to the heart is suddenly blocked

Cardiac syncope becomes more common as people get older. For example, it is estimated that a third of people aged 60 years or over who have fainted may have fainted as a result of a heart problem. 

Parkinson's disease
A long-term neurological condition that affects the way the brain co-ordinates body movements, including walking, talking and writing.
Spinal cord
The spinal cord is a column of nervous tissue located in the spinal column. It sends messages between the brain and the rest of the body.

Page last reviewed: 13/07/2011

Some types of fainting (syncope) are medical emergencies. Cardiac syncope, for example, which is where fainting is caused by an underlying problem with your heart, may require urgent medical attention.

Your GP will be able to diagnose other types of fainting, such as situational syncope, which is fainting caused by a bodily function or activity, such as sneezing or laughing. What type of fainting you have will determine whether you need to have any treatment. 

Emergency medical advice

Fainting can sometimes be mistaken for a serious medical condition, such as a stroke. A stroke is a medical emergency that occurs when the blood supply to the brain is interrupted.

You should dial 999 immediately to request an ambulance if you suspect that you or someone else is having a stroke.

The main symptoms of stroke can be remembered with the word FAST, which stands for Face-Arms-Speech-Time.

  • Face: the face may have fallen on one side, the person may not be able to smile, or their mouth or eye may have drooped.
  • Arms: the person with a suspected stroke may not be able to raise both arms and keep them there due to arm weakness or numbness.
  • Speech: the person may have slurred speech.
  • Time: it is time to dial 999 immediately if you see any of these signs or symptoms.

You should also dial 999 to request an ambulance if someone faints and does not regain consciousness after a minute or two.

When to see your GP

Most cases of fainting are not a cause for concern, but you should see your GP after you have fainted, particularly if you:

  • have no previous history of fainting
  • experience repeated episodes of fainting
  • injure yourself during a faint
  • have diabetes, which is a condition that is caused by too much glucose in the blood
  • are pregnant
  • have a history of heart disease, which is where your heart's blood supply is blocked or interrupted
  • experienced chest pains, an irregular heartbeat or a pounding heartbeat before you lost consciousness
  • experienced a loss of bladder or bowel control
  • took longer than a few minutes to regain consciousness

Information for your GP

To help your GP to make an accurate diagnosis, you should give them as much information as possible about the circumstances surrounding your fainting episode. Possible useful information includes:

  • where you were and what you were doing just before you fainted
  • whether you experienced any symptoms or unusual sensations before you fainted, such as sweating
  • whether there is a history of heart disease in your family
  • whether you have experienced previous episodes of fainting
  • whether you are taking any medication
  • how long you were unconscious for
  • whether you experienced any symptoms after you regained consciousness, such as weakness or confusion

STARS, a charity in the UK, for people who experience fainting, have produced a blackouts checklist to give you advice if you're preparing for an appointment with your GP. It also contains information about what to expect if you have a hospital appointment.

Assessment

During the assessment, your GP will ask about the circumstances surrounding your fainting episodes and your recent medical history. They may:

  • Measure your blood pressure using a sphygmomanometer. This device has an inflatable cuff that goes around your upper arm and a scale of mercury, like a thermometer, as a pressure gauge.
  • Listen to your heartbeat using a stethoscope. This instrument has a metal disc that is placed on your chest and a pair of ear pieces that your GP uses to listen to your heartbeat

Your GP will need to check that the fainting was not caused by problems with your heart. If there are any signs of a heart problem, such as an unusual heartbeat, they may suggest that you have an electrocardiogram (ECG).

Electrocardiogram (ECG)

An ECG records the rhythm and electrical activity of your heart. A number of small, sticky patches called electrodes are placed on your arms, legs and chest. Wires connect the electrodes to an ECG machine.

Every time your heart beats, it produces tiny electrical signals. The ECG machine traces these signals on paper, recording any abnormalities in your heartbeat.

An ECG is usually carried out at a hospital or GP surgery. The procedure takes about five minutes and is painless.

Carotid sinus test

Your GP may massage your carotid sinus to see whether it makes you feel faint or lightheaded. Your carotid sinus is a collection of sensors in the carotid artery, which is the main artery in your neck that supplies blood to your brain.

If the carotid sinus massage causes symptoms, it may indicate that you have carotid sinus syndrome. See Fainting - causes for more information about this condition.

Blood tests

Blood tests may be carried out to rule out conditions such as diabetes or anaemia. Anaemia is a condition where the body does not produce enough oxygen-rich red blood cells.

Tilt-table test

Your GP may suggest you have a test called the tilt-table test to rule out orthostatic hypotension as a possible cause of your fainting. If your GP does not have access to a tilt-table, you may be referred to a specialist, for example at a hospital, to have this test.

During the test, you will be strapped to a table that is tilted upwards. If the sudden move from a horizontal to a vertical position makes you feel lightheaded, it is likely that you have orthostatic hypotension.

Alternatively, your GP may measure your blood pressure while you are lying down and again after you stand up. You may have orthostatic hypotension if your blood pressure falls after you stand up.

If you have orthostatic hypotension, you may be asked further questions to help determine the cause. For example, it can sometimes occur as a side effect of some medications.

Diagnosing the cause

If tests are unable to find a serious underlying cause for your fainting, it is likely that you have experienced vasovagal syncope (see Fainting - causes). If this is the case, further testing and treatment will probably not be needed.

If tests reveal that there is an underlying cause of your fainting, such as a heart problem or orthostatic hypotension, your GP may recommend treatment (see Fainting - treatment).

Page last reviewed: 13/07/2011

Treatment for fainting (syncope) will depend on whether there is an underlying cause. See Fainting - causes for more information about the possible causes of fainting.

Treating the underlying cause

If your GP finds an underlying cause for your fainting, treating it should help prevent further fainting episodes. For example, if you are diagnosed with type 2 diabetes (where there is too much glucose in the blood) you may be advised to take regular exercise and eat a healthy diet.

If you are diagnosed with a heart condition, you may need to have further tests and treatment. For example, there are several different medicines that can be used to treat heart disease, which is where your heart's blood supply is blocked by a build-up of fatty substances in the main blood vessels.

Treating neurally mediated syncope

Neurally mediated syncope, also called reflex syncope, includes:

  • vasovagal syncope
  • situational syncope
  • carotid sinus syndrome

Treatment for neurally mediated syncope involves avoiding any possible triggers. If you are not sure what caused your fainting episode, your GP may suggest that you keep a diary of any symptoms you experience and what you were doing at the time that you fainted, to help identify possible causes.

Vasovagal syncope

Vasovagal syncope occurs when something triggers a temporary malfunction in your autonomic nervous system. This is the part of the nervous system that is responsible for regulating many of the body’s automatic functions, such as heartbeat and blood pressure.

In most cases of vasovagal syncope, further treatment is not required. However, you may find it useful to avoid potential triggers, such as:

  • spending a long time on your feet
  • hot and stuffy environments

If you know that injections or medical procedures (such as blood tests) make you feel faint, you should tell the doctor or nurse beforehand. They will then be able to make sure you are lying down during the procedure.

Situational syncope

Situational syncope is caused by a bodily function or activity that places a sudden strain on your autonomic nervous system, such as sneezing or laughing. There is no specific treatment, but avoiding the triggers may help. For example, if coughing has caused you to faint, it may be possible to suppress your urge to cough and therefore avoid fainting.

Carotid sinus syndrome

Carotid sinus syndrome is where pressure on your carotid sinus causes you to faint. Your carotid sinus is a collection of sensors in the carotid artery, which is the main artery in your neck that supplies blood to your brain. You can avoid fainting by not putting any pressure on your carotid sinus, for example, by not wearing shirts with tight collars.

In some people, carotid sinus syndrome can be treated by having a pacemaker fitted. A pacemaker is a small, battery-operated device that is inserted into your chest to help your heart beat regularly.

See the Health A-Z topic about Pacemaker implantation for more information about the procedure.

Treating orthostatic hypotension

Orthostatic hypotension is a type of fainting that occurs when you stand up suddenly. This is because your nervous system does not stabilise your blood pressure quickly enough. By avoiding anything that lowers your blood pressure you should be able to prevent fainting. For example, you should:

  • make sure you do not get dehydrated, for example, by limiting how much alcohol you drink
  • avoid medication that can lower your blood pressure, but do not stop taking a prescribed medication unless you are advised to do so by your GP or another qualified healthcare professional who is responsible for your care
  • Your GP may advise you to take midodrine if you suffer from orthostatic hypotension.

See the Health A-Z topic about Low blood pressure - treatment for more information and advice about orthostatic hypotension.

If someone is about to faint

If you know or suspect that someone is going to faint, you should help the person to lie down, preferably in a position where their head is low and their legs are raised.

If it is not possible for the person who is feeling faint to lie down, sit them down with their head between their knees. Gently, but firmly, push their head down while they try to push their head upwards. This will encourage the blood to flow to their brain, reducing their symptoms and helping them to recover more quickly.

Physical counterpressure manoeuvres

Physical counterpressure manoeuvres are movements that are designed to raise your blood pressure and prevent you losing consciousness. One study found that just under a third of people who fainted regularly who were trained in physical counterpressure manoeuvres fainted within a year, compared with half of those who were not trained in using these measures.

Physical counterpressure manoeuvres include:

  • crossing your legs
  • clenching the muscles in your lower body
  • squeezing your hands into a fist
  • tensing your arm muscles

You need to be trained in how to carry out these movements correctly. You can then carry them out if you experience any symptoms that suggest you are about to faint, such as feeling lightheaded.

If someone has fainted

If a person faints and does not regain consciousness within one or two minutes, you should put them into the recovery position. To do this, you should:

  • place the person on their side so they are supported by one leg and one arm
  • open their airway by tilting their head back and lifting their chin
  • monitor their breathing and pulse continuously

You should then dial 999 to request an ambulance and stay with the person until medical help arrives.

Driving

If you have fainted, it could affect your ability to drive. You should not drive again until you have been assessed by a healthcare professional. .

Safety at work

If you have fainted, it may also affect your safety at work or the safety of others. For example, if you operate machinery, it may be dangerous to continue to use it if you are likely to faint again.

The healthcare professionals who diagnose and treat your condition will be able to explain to you whether it is likely to affect your work. If it is, you should speak to your health and safety representative.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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