I have what are apparently know as 'silent' labours, which means I don't feel the contractions at all, just a little bit of tightening, I didn't realise I was in labour until I was 7cm with both DC, DC1 I was in for an obstetrics appointment, stood up to see the the Obs, my waters broke all over the waiting room and when she examined me I was 7cm, strolled through to the delivery suite then sat around reading the paper for a couple of hours saying to DH, 'Im sure I'm meant to be doing something'. Midwife let me know when it was time to push, crowning was a bit stingy but not too bad. No stiches, tears or grazes.
DD homebirth, midwife said to call if I felt anything given how DS' birth went. Felt a bit twingey so she came over, 7cm again so she stayed, felt like a total fraud as I was just sitting round drinking tea, even suggested to her we put a film on to pass the time, when I got to 9cm she called the other Midwife, and after about 20 mins, I stood up, let out a roar, and out shot DD, the midwives weren't expecting it as they had to run across the room to catch her. No pain or pushing at all.
So even though rare, it can be a pain-free experience (and I was expecting it to be utterly horrendous).
Reading these makes me realise how very, very, lucky I am!