They say laughter is the best medicine, but not in Kay Underwood's case. In fact, a fit of the giggles is all it takes to cause the 20-year-old student to collapse on the spot.
Miss Underwood suffers from cataplexy - a muscular weakness triggered by emotion which can lead to anything from slackening of the facial muscles to total collapse.
Exhilaration, anger, fear, surprise, awe and even embarrassment can also cause similar reactions, but for Miss Underwood, it is a fit of the giggles which does the trick.
Victims are often left paralysed for several minutes, although they always retain the ability to hear what is going on around them.
Today she told how the condition is no laughing matter - and once caused her to collapse more than 40 times in a single day.