What is it?

Ask Nicolas Sarkozy. The French president suffered from a vasovagal syncope while jogging last month — it’s the medical term for a simple faint. “Vaso” refers to blood vessels; “vagal” to the vagus nerve, which is capable of slowing the heart rate. Should it do so, blood pressure falls abruptly and less oxygen flows to the brain. The result is a brief loss of consciousness.

Why does it occur?

Because the vagus nerve has detected that the heart is overexerting itself. Triggers for such a slowdown include standing for long periods (the “guardsman’s faint”), stress and excessive exertion, and are more likely to happen if someone is tired or dehydrated. The faint is an emergency measure by the body to restore oxygen levels: even low blood pressure can get sufficient supplies of oxygen to the brain because the heart no longer has to work against gravity.

What are the warning signs?

They include sweating, dizziness and pallor. If you do not then lie down or sit down for five or 10 minutes, a faint usually follows. To help prevent it, never exercise excessively if tired, always drink lots of water and try to wind down slowly. For more information visit tinyurl.com/n932eq

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