Jumping Frenchmen of Maine Disorder.
The typical response to being startled -- muscles tense, heart pounds, senses go on alert -- lasts only a few seconds. But in this disorder, first observed in 1878 among French-Canadian lumberjacks in the Moosehead Lake area of Maine, the reaction is greatly exaggerated.
Sufferers jump, twitch, flail their limbs and obey commands given suddenly, even if it means hurting themselves or a loved one. It's also been observed in factory workers in Siberia and Malaysia. Some experts believe it's a genetic mutation that blocks glycine, a neurotransmitter that calms the central nervous system's response to stimuli.
Others think it's more psychological than neurological, and perhaps part of a heightened defense mechanism from living and working in close quarters.