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Blackouts, light-headedness and fainting


Vasovagal syncope (fainting) or pre-syncope (near fainting or light-headedness) is the most common cause of transient loss of consciousness. The condition is due to an exaggerated neurological reflex of the autonomic (involuntary) nervous system which controls multiple organs including the heart and blood vessels. The syncope reflex causes a slowing of the heart rate and a reduction in blood pressure. This combination causes a temporary reduction or cessation of blood flow to the brain thus causing near or complete loss of consciousness.

The syncope reflex commonly has a trigger which can be physical or emotional. Common examples include hot, crowded environments, unpleasant situations (for example, having a blood test) or even everyday actions like urinating, opening bowels, coughing, laughing or simply standing up from a sitting or lying position. The resulting loss of consciousness can occur without warning but may be preceded by light-headedness, nausea, sweating or dizziness. The period of unconsciousness may last from a few seconds to several minutes but recovery is typically prompt and complete.


Why should I see a specialist at LHRG?

Vasovagal syncope is not dangerous and has an excellent prognosis. Consultation with one of our specialists is particularly valuable if symptoms are frequent, debilitating, occur without warning, cause injury or if they manifest after the age of 40 years. With recurrent symptoms it is always important to exclude structural and electrical abnormalities which may require specific treatment.




Most patients who suffer from vasovagal syncope will improve with simple lifestyle, dietary and behavioural modification. Some patients may require additional support with medication and a small minority may even benefit from pacemaker implantation.


The choice of treatment offered to our patients is tailored to the individual's needs and is largely directed by a consultation with one of our specialists and the results of simple non-invasive tests.

Warning signs

We would particularly recommend early referral to our specialists if you or your patient suffers with loss of consciousness or palpitations in the context of:


i) Known heart disease such as a heart attack, coronary disease or heart failure,

ii) an abnormal ECG,

iii) Family history of young, unexpected death

iv) Syncope on exertion or

v) Syncope in a lying posture.

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The material on this site is for informational purposes only, and is not a substitute for medical advice, diagnosis or treatment provided by a qualified health care provider.