Fainting is medically called syncope. It happens when you briefly lose consciousness because the blood flow to your brain reduces. In most cases, the loss of consciousness is very brief and individuals recover quickly.
Here, we’ll explore the most common causes of fainting, getting a diagnosis and how to prevent and/or treat syncope.
First, it helps to understand some of the common words that are used in conversation when talking about fainting.
Fainting vs blacking out
Blacking out and fainting (syncope) both refer to a loss of consciousness. However, not all blackouts are due to syncope.
You may black out due to drinking too much alcohol, drug abuse, epilepsy, head trauma or extreme psychological stress.
Fainting vs dizziness
It’s common to experience dizziness just before fainting, but feeling dizzy doesn’t always mean that you’re about to faint. What’s more, the causes of dizziness and syncope can be different.
Syncope happens when blood flow to your brain drops. Although dizziness can be caused by a drop in blood flow to your brain, it can also be caused by inner ear problems that don’t affect blood flow, such as benign paroxysmal positional vertigo (BPPV) or an inner ear infection.
Types and causes of syncope
Vasovagal syncope
The most common type of syncope is vasovagal syncope, which is often called a simple faint. This sudden drop in blood flow to the brain can be triggered by several different things, including:
- Dehydration
- Emotional stress
- Pain
- Phobias, eg fainting when seeing blood
- Standing up for a long time
A simple faint often comes with warning signs just before fainting. These may include feeling:
- Dizzy
- Hot
- Lightheaded
- Nauseous
- Sweaty
Immediately before fainting, you may notice your vision starting to go dark. After fainting, recovery is usually very quick and you can often get on with your day as normal.
Orthostatic syncope
This occurs when you move from lying down or sitting to standing. Blood flow to your brain suddenly drops because your body does not adapt quickly enough to the effect of gravity on your blood flow.
This is more likely to happen if you’re dehydrated, taking certain medications (eg blood pressure-lowering drugs) or have problems with the nerves that help regulate your blood pressure due to an underlying condition, such as diabetes or Parkinson’s disease.
When to see a doctor about syncope
If you faint with no obvious reason or are repeatedly fainting, see your GP. This is particularly important if you:
- Had chest pain or palpitations before fainting
- Have an underlying heart condition
- Have a family history of sudden cardiac death
- Fainted while exercising
- Fainted while sitting or lying down
Diagnosing the cause of syncope
The first step to uncovering why you fainted usually involves your doctor taking a detailed medical history and finding out exactly what you were doing and how you felt just before fainting, as well as how you felt afterwards.
Your doctor will usually examine you, listen to your heart, check your blood pressure while lying down and standing, and perform an ECG (electrocardiogram).
Based on these results, you may need further investigations, such as ECG monitoring over 24 hours, several days or longer.
If these initial tests do not find a cause and fainting episodes continue, an implantable loop recorder (ILR) may sometimes be recommended, particularly for people with infrequent but unexplained syncope or suspected cardiac syncope.
An ILR can record your heart rhythm over months or years and may help identify an abnormal heart rhythm occurring at the time of a faint.
This involves inserting a small heart monitor under the skin of the chest. It is a minor procedure performed under local anaesthetic, which means you’ll be awake but the area will be numbed.
Treating syncope
If you experience vasovagal syncope (a simple faint), lifestyle changes can help prevent further episodes. These include staying well hydrated, recognising the warning signs and immediately sitting or lying down, and, where possible, avoiding situations that trigger your fainting.
If you’re standing for long periods of time, there are also certain movements you can perform to increase blood supply to your brain and help prevent blood from pooling in your legs. These are called physical counterpressure manoeuvres (PCMs). They tense your muscles to improve blood flow and include:
- Arm tensing — hooking your fingers together in front of your chest and pulling your arms outward in opposite directions
- Buttock and fist clenching
- Leg crossing — tightly crossing one leg over the other while tensing the muscles in your legs
- Squatting
If you have low blood pressure and staying well hydrated is not enough to prevent fainting, your doctor may recommend other measures or, in some cases, medication to increase your blood pressure.
If you have a heart condition, treatment depends on the specific cause. For example, some slow heart rhythms or electrical conduction problems may need a pacemaker, while other arrhythmias may be treated with medication, catheter ablation or other treatments.
If you have unexplained or recurrent fainting, it is worth booking a consultation for further assessment.
