Kay Underwood, 20, has cataplexy, which means that almost any sort of strong emotion triggers a dramatic weakening of her muscles. Exhilaration, anger, fear, surprise, awe and even embarrassment can also cause sufferers to suddenly collapse on the spot.

Kay, of Barrow-upon-Soar, Leicestershire (UK), who was diagnosed with the condition five years ago, once collapsed more than 40 times in a single day. She said: "People find it very odd when it happens, and it isn't always easy to cope with strangers’ reactions. "

Like most cataplexy sufferers, Ms Underwood is also battling narcolepsy - a condition that makes her drop off to sleep without warning. Narcolepsy affects around 30,000 people in the UK and about 70 per cent of them also have cataplexy.