Dizziness - Causes of feeling faint

Authored by Dr Mary Harding, 26 Jul 2017

Patient is a certified member of
The Information Standard

Reviewed by:
Dr Louise Newson, 26 Jul 2017

People who feel faint often say they feel "light-headed" and feel as if they may collapse unless they sit or lie down. This is sometimes described as feeling dizzy. Most of us can remember times when we have felt like this. For example, when we have been ill with a high temperature (fever), very hungry, or very emotional. However, some people have repeated episodes of feeling faint without an obvious explanation such as a fever.

Causes include the following:

Orthostatic hypotension

This means your blood pressure drops when you sit up from lying, or when you stand up from sitting or lying. In particular, if you jump up out of bed after a night's sleep. The fall in blood pressure is just for a short time as the blood pressure quickly adjusts to your new posture. However, in some people the fainting feeling can be more severe and last for a few minutes. This problem tends to get more troublesome as you become older.


The main symptom of anaemia is tiredness. However, if you have anaemia you may not get sufficient oxygen to the brain. This can make you feel light-headed.

Arrhythmias and other heart problems

An arrhythmia is an abnormal heart rhythm. It occurs when the heart may suddenly beat too fast, too slowly, or in an abnormal way. There are various causes. One of the symptoms of an arrhythmia is to feel faint or light-headed as there may be a sudden decrease in blood supply to the brain as the arrhythmia develops. See separate leaflet called Abnormal Heart Rhythms (Arrhythmias) for more details.

Various other heart disorders may cause a reduced flow of blood to the brain and cause you to feel faint or light-headed.


In particular, if you have anxiety with panic attacks you can feel light-headed. This can get worse if you over-breathe (hyperventilate) due to the anxiety or panic attack.


Feeling faint and/or light-headed is sometimes a side-effect of some medicines. It is always worth reading the information leaflet that comes in the drug packet to check if dizziness is a recognised side-effect.

Further reading and references

  • Vertigo; NICE CKS, April 2010 (UK access only)

  • Huh YE, Kim JS; Bedside evaluation of dizzy patients. J Clin Neurol. 2013 Oct9(4):203-13. doi: 10.3988/jcn.2013.9.4.203. Epub 2013 Oct 31.

  • Kaski D, Bronstein AM; Making a diagnosis in patients who present with vertigo. BMJ. 2012 Sep 3345:e5809. doi: 10.1136/bmj.e5809.

  • Post RE, Dickerson LM; Dizziness: a diagnostic approach. Am Fam Physician. 2010 Aug 1582(4):361-8, 369.

  • Kerber KA, Baloh RW; The evaluation of a patient with dizziness. Neurol Clin Pract. 2011 Dec1(1):24-33.

Hello, I’m a 32 yo male with type 1 diabetes and for the last 2 months I’ve experienced daily episodes of lightheadedness. I’ve seen an ENT, a neurologist and a cardiologist and all of them have...

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