yes I know what it's like. It haunted me and cost me many, many nights' sleep when pg. I had an epis the first time but was sewn up quite tight (sorry TMI) afterwards and knew it was a dead cert I'd tear the 2nd time. It terrified me and the thought just made me squirm. I did tear, but I literally did not feel it happening at all. Weirdly I actually really enjoyed the sensation of pushing him out. I remember the pain of contractions but no pain pushing him out at all. It probably helped that I felt I'd missed out on the actual pushing last time, because of my epidural, so wanted to feel that sensation this time.
I healed much, much better after the natural tear.
I totally understand why you're freaking out, and I did too. It's a horrible thought. But the reality was honestly fine and, I repeat, I literally did NOT feel it happen.