C. Ann,
Claustrophia is a variant/form of an anxiety disorder. My mom has it and probably didn't develop it until her 40s. Now she has it very bad but is okay with managing it.
It could get worse, stay the same, or never happen again. I don't know what causes it. Sometimes it just has to do with how tired you are on a particular day, how you are feeling, and then having all the *wrong* things happen.