Once I hit 10 cms and they had me sit up to start pushing, I started dry heaving (I would have thrown up but I had nothing in my system at that point since I had labored for so long). It wasn't fun but only lasted for a minute, maybe 2 and then my body had adjusted to the new position I was in and my mind went to "get this baby out" mode.
The nurse said you just have so many hormones rushing through your body that sometimes you get a little nauseous.