vaginapagina | no idea how to describe my fears/issues

(with no preamble) I'm absolutely horrendously paralyzingly terrified of anal sex, or of any contact with my anus. Now, normally this would not be an issue, but tonight my boyfriend and I were having sex and he accidentally slipped out of my cunt. He slid into my ass crack instead (again, by complete accident). I reacted by wriggling out from under him (I was on my stomach, with him lying on top of me) and ran to the bathroom. Cried for a fair while, while he flipped out and went outside to smoke a cigarette. He's such a sensitive guy, so he hates it when I get so freaked. Tonight was worse; I ended up obsessing in the bathroom over what I could use to hurt myself. I've rarely been this bad after such a mistake.

A little background: I'm _not_ a prude by any stretch of the imagination. I've been having sex for nearly seven years. I enjoy different positions, etc, and am into fairly heavy bondage (not blood-play level but I definitely like hardcore bruising). I'm a "recovering" (ha!) eating disordered 22 year old woman who just freaked the fuck out about...well, nothing. I hate that I freak about anal play/anything remotely in that area. I don't know why I hate it; I wish I didn't. I'm not a non-communicative person; I tell my boyfriend anything/everything in the bedroom. He knows my upset with anal play, and tries his hardest to avoid it. Tonight was an honest accident, and I just...did my thing. Ugh. *hating self right now*

I guess what I'm getting at is...advice? Does anyone else freak out like this, so I would know I'm not quite as alone/utterly fucked up as I feel? Any advice to stop freaking the fuck out, or opinions on _why_ I freak out? _Anything_? Feelin pretty shitty right now.