Why am I seeing stars after bumping my head?

Asked by: Daniel Tilly, Market Harborough

The stars you see are actually neurons in your visual cortex firing spontaneously. This occurs when their oxygenation level changes abruptly either because you have stood up too quickly or because your brain has been suddenly accelerated by a sharp blow, sloshing blood into or out of the capillaries.

The neurons closest to capillaries are affected first and, if it happens fast enough, they fire well before the surrounding neurons. This results in isolated signals that your brain interprets as lights.

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• Why are bald heads so shiny, when the skin elsewhere on your body isn’t?

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