Claustrophobia?

One of the elevators I was in at work got really crowded. I had to rush out and sit down. I had one person ask me if I was ok and I didn't want her to "call someone from my office for me". :( I didn't even realize I was shaking until this guy pointed it out and he thought I was shaking because I was cold...When in the hell did I develop claustrophobia? That's the last thing I need with Metro as bad as it can be here.