Too strong of an imagination?

[C0FFINCASE]

Anxiety as a result of your phobia. It's not something the average person has to deal with, but it could be way worse. Learn to meditate. Especially if you are in large spaces (e.g. outside, wide enough rooms, etc.), you shouldn't be having these panic attacks. You need to calm yourself down and remind yourself that you are free/whatever is the cause of your claustrophobia.
I'm not entirely sure how you'd go about meditating it away if you were actually in a small room. I guess merely imagining that you're in a large room or constantly reassuring yourself that you're safe.

Or break your phobia. Begin a regiment of placing yourself in situations where you must face your fear, stepping up the severity as you learn to deal with it.

Everyone does face thoughts not necessarily fear scenarios, but the random imaginary scenario fly's through your head as your sitting some where, happens.