Just to say I had my first DD in Feb. I was really, really scared about tearing (though not for any good reason like you just irrational fear), and was much more scared of that and of being stitched than actual labour. I am also known as a bit of a wimp with a low pain threshold by my family!
When it came to it I was so overwhelmed (not in a bad way just whole body taken over by) the pushing contractions, that I didn't even notice the crowning (no 'ring of fire). When the MWs said the head was out I was amazed! And I hadn't had any pain relief.
I had a small tear as DD had her hand by her head. I couldn't feel it at all, had no idea it happened. I was then terrified about the stitches, but I grabbed the G and A (which I hadn't used in labour) and went nuts on it. Instead of being aware of the stitches I had a lovely 10 mins totally high off my face while looking at DD who DH was holding.
I never felt a single bit of jip from the stitches afterwards - not even when going to the loo.
Obviously me experience not totally typical, but just to say that labour is so different from any other experience down there, there's so much going on, your body and mind are working differently than normal so you will be surprised by what bothers you and what doesn't.
Good advice though to talk over your fears in advance especially because of the horrible experience you had before.