Ever test a phobia and push it to the limit? If a person with claustrophobia were stuck in a cave or mine or cavern what would happen?

I assume their panic attack would get so severe that they would do great bodily harm to themselves trying to escape, pass out, or have a heart attack.  That kind of phobia isn't one that one can say, "oh, just get over it".  Most phobias are deep rooted.  Some can be traced to a traumatic occurance in a person's past.