A blackout or transient loss of consciousness (TLOC) can be due either to a problem with the heart, the circulation or the brain. Fainting can occur in healthy individuals, but disorders of the heart, circulation and brain should be considered. 



Cardiac causes of loss of consciousness include slow heart rates (bradyarrhythmias) and fast heart rates (tachyarrhythmias).

 

Brain-related causes include epilepsy. Strokes and mini-strokes (transient ischaemic attacks, TIA's) do not generally cause loss of consciousness. It can also occur in patients with metabolic disorders, such as in diabetics on insulin or diabetic drugs.

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A useful resource for further information is the website for the Syncope Trust and Reflex Anoxic Seizure (STARS)

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