Feeling faint – 5 top tips to help with syncope

Written by: Dr Boon Lim
Edited by: Cal Murphy

It is known by many names: fainting, swooning, blacking out, passing out – the list goes on. You may know someone who has lost consciousness in a crowded place or blacked out while having an injection; perhaps it has happened to you. What causes this phenomenon? Why are some people prone to fainting? And what can you do to prevent it? Leading cardiologist and syncope expert Dr Boon Lim gave us his five top tips to help with syncope.

What is syncope?

Syncope (pronounced sin-cope-pee) is the medical word for fainting or blacking out. This loss of consciousness is caused by several factors, including low blood pressure and the heart beating less strongly than normal. Another factor is a phenomenon called reduced peripheral vascular resistance. This basically means that the blood vessels are less “tightly constricted” and as these vessels relax, particularly in the legs, significant amounts of blood (up to 800 ml) can pool in the legs due to gravity.

Pooling can also occur in the stomach and intestinal bed – which explains why some people may feel very lightheaded or sleepy after a particularly large or carbohydrate-rich meal. This form of syncope is termed vasovagal syncope and is generally a safe condition, and most patients can significantly improve symptoms by adhering to simple strategies which are outlined at the end of this article.


However, there are forms of syncope which should prompt urgent referral to your doctor. The red-flag symptoms for syncope include:

  1. Fainting during exercise (in mid-exertion, rather than immediately after exertion)
  2. Fainting without any warning signs, usually resulting in injury.
  3. Fainting when you have had a past history of a heart attack or heart rhythm abnormalities.


If you have had any of these symptoms, please do not wait – see your doctor as soon as possible!


What are the warning signs of vasovagal syncope?

Due to blood pooling in the lower limbs, the heart is receives less blood (15-20%) than usual, and therefore, with each heartbeat, less blood is pumped, which leads to activation of a fight-or-flight response in the form of a burst of adrenaline (sympathetic surge).

The adrenaline surge is what typically triggers your warning symptoms before you faint. These symptoms include:

  • Nausea
  • Light-headedness
  • Palpitations
  • Anxiety
  • Sweatiness
  • A need to cool down or get breath of fresh air
  • Clamminess
  • Feeling hot

People who faint typically do so in certain situations, such as:

  1. When standing for prolonged periods, e.g. in a crowded commute
  2. When dehydrated
  3. When feeling unwell, with an intercurrent illness, such as diarrhoea and vomiting, or a chest infection
  4. When getting up very rapidly from a seated or lying position


Top 5 tips for preventing fainting when you are feeling acutely unwell:

If you are experiencing the symptoms above, please do the following immediately:

  1. Sit down or lie down and elevate your feet. Doing so will allow some of the blood that has pooled in your lower limbs to flow back to your heart and brain and restore normal blood pressure.
  2. Perform isometric counter-pressure exercises – this means tensing your calves, quads and gluteal muscles (clenching your buttocks). Doing so will externally compress the deep veins of your feet and send some of the pooled blood back into the central circulation to the heart and the brain to improve blood pressure.
  3. Keep adequately hydrated, aiming for 2.5-3.0 L a day.
  4. Avoid situations that you recognise to be clearly provoking of syncope.
  5. Consider compression stockings, which again serve to improve blood flow from the lower limbs back to the rest of the body.

By Dr Boon Lim

Dr Boon Lim is one of London's leading cardiologists and electrophysiologists. He specialises in heart rhythm disturbances, pacing and syncope at Imperial College and at his Harley Street clinic. He leads the established Imperial Syncope Diagnostic Service at Hammersmith Hospital and is frequently invited to national and international meetings to share his experience. He has a special interest in the mapping and ablation of atrial fibrillation (AF) and is highly-skilled at using modern 3-D mapping technologies. Dr Lim was awarded several prestigious prizes during his medical training at Cambridge University where he obtained a double First Class Honours Degree. He has continued his passion for education and research serving as an Honorary Senior Lecturer at Imperial College where he supervises several PhD students.

Dr Lim is very actively engaged in all aspects of research with a particular interest in developing the best techniques for treating atrial fibrillation. He is invited to speak both nationally and internationally to discuss his findings and to teach other physicians about the best techniques for complex mapping and ablation of atrial fibrillation and other complex arrhythmias. He leads a very active syncope research team based at the Imperial Syncope Diagnostic Unit and is looking to improve healthcare delivery for patients through use of effective online education to help improve the quality of life for patients across the UK. 

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