Claustrophobia...mostly.
Basically, I'm fine in a smallish space unless I feel my limbs are pinned and unable to move. Didn't really notice I had this phobia until I was young and someone put a sleeping-bag over my head for a laugh and I flipped out and started screaming and trying to tear the bag in half.
Needless to say, it has not happened since.
Weirdly, though, even minor things set it off. I was sleeping in a small bed with my girlfriend and I was against the wall. She leant close to me, and suddenly I got all anxious that I couldn't move my limbs. Then, when I thought about it, I just plain started freaking out. I just went perfectly still and waited for her to turn over, while hyperventilating, afriad of waking her up and afraid of being trapped against the wall. It was odd, I knew I could easily just push her over, but the sensation of having my limbs 'stuck' made me go all "THE WAAAAAAAAALLSSSSSS...SO MANY WAAAAAAAAAAALLSSSS..."