Vasovagal response: A cause of near-fainting?

I recently hit my knee on a hard corner. Immediately, I had intense pain followed by a prickly feeling in my leg. Then I felt hot, dizzy, nauseated and couldn't see or hear properly. What happened?

- No name given / Australia

Answer

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Peroneal nerve

It's likely that you struck your leg in the area where the peroneal nerve lies near the surface of the skin — which is on the outside of the shinbone just below the knee. If you bump your peroneal nerve, it usually results in tingling numbness and often pain in your foot and leg. The other symptoms that you describe are referred to as a vasodepressor or vasovagal response.

Intense pain, such as due to hitting your knee on a hard corner, may cause a temporary, exaggerated vasovagal response by your autonomic nervous system. As a result, your heart rate and blood pressure drop, which reduces blood flow to your brain. This results in a feeling of warmth, lightheadedness, dimming of vision and hearing, and even fainting (vasovagal syncope).

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