It can cause considerable complications to the lives of those who have it. Take the story of Jay Fenton of Annapolis, Md., a Vietnam veteran whose experiences led to a paralyzing fear of crossing bridges.
"I thought I was losing control," he says. "My heart was pumping. I was dizzy and lightheaded, and I thought I was going to pass out."
So severe was Fenton's phobia that he could not go on vacation with his family for fear of crossing a bridge.
When he eventually did need to cross one, he had to ask someone to drive him from one end to the other -- after he locked himself in his trunk.