Why do i faint?

1 Jan 2023 | Dr Boon Lim & Dr Melanie Dani

Understanding fainting

Fainting, also known as syncope (pronounced “SIN-COPE-PEE”), is a temporary loss of consciousness that can leave us feeling scared, bewildered and concerned. It’s a peculiar and often disturbing experience that often catches us off guard, leaving us wondering why it happened, and on occasion, very fearful about whether it means that there is something fundamentally wrong with our health. In most cases, fainting is something that has an easily-identifiable underlying cause, and this article explores some of the reasons why you may be fainting, and delves into the triggers, and what you can do to prevent this. 

The basics of fainting

Fainting occurs when there is a temporary reduction in blood flow to the brain, leading to a brief or transient loss of consciousness. Our brain requires a constant supply of oxygen and nutrients carried by the blood to function properly. When this supply is compromised, our brain reacts by causing us to faint, essentially allowing the body to reset and restore blood flow.

Are there any causes of loss of consciousness or fainting which are not to do with reduction in blood flow to the brain?

Occasionally, a brief loss of consciousness can occur for other reasons unrelated to blood flow reduction to the brain. Some other causes of these momentary loss of consciousness include epilepsy, or a primary seizure disorder, which is a neurological condition where the brains normal electrical activity is disrupted due to uncontrollable bursts of electrical signals which can cause a transient loss of consciousness. Other reasons for transient loss of consciousness include concussion (for example after a fall) or drug intoxication, or psychogenic pseudosyncope, a condition in which there is an appearance of loss of consciousness without any changes to blood flow to the brain or abnormal electrical activity (seizure) in the brain. 

It is important if you are unclear about your diagnosis that you seek medical professional help with ascertain your diagnosis. 


What can I do to help my doctor make a diagnosis?

It is common with fainting episodes to be frightened and fearful, particularly if you are alone or suffer injury when it occurs. However, do try and think of the following questions, and if possible write down these points, to discuss with your doctor. Some of the aspects of the episode which you describe may be sufficient for your doctor to come up with a firm diagnosis and to initiate a management plan and/or offer reassurance immediately. In other cases, your doctor may wish to start urgently investigating your symptoms. Your fainting specialist will find it helpful to have a video recording of your faints and therefore if this occurs repeatedly and you are in the position of safety when the faint has occurred, do get a family member or friend to record your face, including your eyes, before zooming out to gain an idea of your body posture during the faint, and to continue recording until you have recovered if it is safe to do so.

What are some of the main questions to consider for my doctor?

1. When did you faint ? 

2. What were you doing immediately before (30 seconds before, 5 minutes before, and perhaps the evening/day before)? Did you for example travel recently on a long haul flight, or perhaps had a long evening with lack of sleep due to work/late night?

3. How did you feel before you fainted? Did you feel nauseous, dizzy, lightheaded, sweaty, palpitations, anxious ? 

4. What was the environment in which you fainted like? Was this in a warm crowded place like a train/bus? 

5. Did you faint following a particular situations or activity? For example did you faint after running or exercising? Or perhaps after passing urine? 

6. How long did it take you to recover? Were you back to normal within 10 seconds, 30 seconds, or 30 minutes after coming round from your faint? 

7. Did you injure yourself? 

8. Was someone with you when you fainted? If they were, please ask them to describe in detail what occurred immediately before you fainted? A clear description of what occurred in the 10-30 seconds before the fainting can be extremely helpful. If there is no way to describe what happened, try to get the witness to “act out” how you were behaving/moving when you fainted. 

9. How many times have you fainted before? 

10. If you have fainted more than once, consider if there are any common triggers for your symptoms. Some triggers include: Dehydration, heat, standing for long periods, standing up too quickly, lack of rest/sleep, passing urine (particularly in the middle of night), and fear/pain (for example whilst having a medical procedure or during blood taking)

Consider writing down the answers to these questions to discuss with your doctor. Alternatively download the STARS blackout checklist on this link here.


Are there any particular fainting features which suggest a more urgent assessment is needed?

There are particular “red flag” symptoms, which should almost always prompt a very urgent doctor assessment (typically within 24 hours) or even a visit to your local accident and emergency department (if injury occurs)

These include:-

1) Fainting during exercise, for example in mid-run

2) Sudden fainting, without any preceding warning symptoms, particularly associated with injury. 

3) Fainting preceded by extremely high racing heart rate (i.e. palpitations)


What is the most common cause of fainting ?

In a majority of cases, fainting is due to vasovagal syncope. In fact, up to 1 in 2 (50%) of patients may faint in their lifetime, likely from vasovagal syncope. Find out more about vasovagal syncope here

However, there are other causes of fainting, and if you are aware of your diagnosis and want to learn more about how to manage your condition, click on link  below

causes of fainting

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