Funnily enough, most cavers I've met have claustrophobia to some extent, myself included. I have to have sedatives to have an MRI! I do have to psych myself up to crawl through spaces I've never done before, but the sense of achievement I get from overcoming both physical and mental obstacles is amazing. However, there have been times when I chickened out - but gone back later and found the fear was far worse than the actuality.