For most of us, laughter is a happy part of life, but for a UK scientist, it can trigger an extraordinary reaction in which she falls into a trance-like state unable to see or move.

A good chuckle is, unfortunately, the strongest trigger, but she also reacts to everyday feelings such as fear, anger, joy or surprise.
u00a0
Claire Allen, from Cambridge, collapses every time she feels a strong emotion. Each episode can last anywhere between 30 seconds to five minutes.