Karen Snyder used to laugh at her hyperekplexia. Like the obscure breed of "fainting goats" that fall down at any small startle, Snyder will crash to the floor with completely stiff limbs at a knock at the door or a tap on her shoulder.
Seconds later, Snyder's stiff body will relax and she can assess whatever damage has been done.
"I've knocked over displays in stores before. You can't control where you're going to get startled," said Snyder, 34, of Chico, Ariz. "Making cupcakes, I went down with a bag of frosting recently."
"I honestly hold hands with a lot of people these days just to try and stay upwards. It's a weird situation," she said. "I throw anything I'm holding and just fall to the floor."
Snyder first fell at a shock at the age of 19 when someone came into the bathroom while she was in the shower.
"My body jumps just like anybody else's body would jump. ... It's not really a sensation at all. It takes all of a second," said Snyder. "There's no voluntary movement that's available to you but at the same time you're totally conscious."
"It started happen at work, and my bosses were stressed out and said they had to have a doctor say I was cleared to work," said Snyder. "I couldn't do that because they [the doctors] didn't know what was going on."
Twelve years after her first fall, Snyder was diagnosed with hyperekplexia, one of the "startle syndromes" known to run in families.
The condition is so rare that experts can't even estimate how many people have hyperekplexia.
Yet, through Facebook and other social networking sites, families affected by hyperekplexia are starting to unite. Snyder and others recently started The Hyperekplexia Society, and more people are coming to the few doctors who specialize in hyperekplexia for diagnosis.
Snyder even sent a blood sample for analysis to Dr. Rhys Thomas and colleagues at Swansea University in the United Kingdom.
Thomas said Snyder's late-onset hyperekplexia is an unusual case.
"The normal story is that you get diagnosed in birth and it may or may not run in your family," said Thomas.
Babies born with hyperekplexia have a very tough time in the first year of life. Thomas said the exaggerated startle reaction can come at any moment -- triggered by baths or putting a jacket on a child. Children's limbs may be stiff without being startled and toddlers can have trouble walking.
Some children also have learning disabilities or a mild form of autism associated with the condition. But the most serious concern is a child's ability to breathe during a severe startle.
"In very young children, they often get repeated breath-holding, what we call apnea attacks in the first year of life," said Thomas. "They go blue and the parents get very worried, and they take a very big breath at the end."
Parents can try to minimize loud noises in the home, but Thomas pointed out that even expected loud noises can cause the reaction -- such as fireworks on the Fourth of July.