Before (right when it's initiated) or half way through.

Usually I don't want it to happen. Why would you want to do something that makes you feel horrible? I wouldn't call it guilt, but that might be my rational mind talking. Rationally I'm pro concentual sex 100% and briefly worked at a sex shop. That being said, I'm really bad at being in touch with my emotions. It's like sex or anything sexual is a massive taboo. "This shouldn't be happening" "this isn't right" are things that go through my head. Imagine being told to torture an animal. That's a very similar feeling when it's at it's worst feelings wise. So yeah, I guess guilty works.