There are two occassions that I have been hit by a man. In the face.
The first time, it was pitch black, so I didn't see it coming. And it was several hits, each delayed by 7 seconds or so--which can seem like a lifetime when you can't see if there's more where that came from.
That first hit, there isn't pain, it's more like you felt a wallop of pressure, but the brain instantly numbifies (yep, it's a word, as of right now) the reality of the pain. And adreniline does wonders to block it out the truth behind the impact as well. I don't know about guys, but for most women, being hit like that is so shocking, the pain is later. You're covering your face, screaming, nothing like this has ever happened, and it's pitch black, so each blow is prepared for in the blind.
Thank God, your sense of self preservation kicks in. You grapple. You clutch. You swing whatever it was you were lucky enough to wrap your hand around.
Later...much later...when you've driven without headlights, fear overruling common sense, and you've arrived to a friend's house...one look in the mirror......THAT'S when you feel the pain.
The following day, there are knots along your cheekbone. Huge knots. Blood vessels burst, the whites of your eyes now red as if possessed. Both eyes black. Everything puffy. It takes about a week for everything to start turning yellow, except the soft tissue under the eyes. That stays black for a long time. The knots can take up to 3 or 4 weeks before you finally don't feel them anymore. And you can't swallow food--but with all the hitting, your brain blocked out you were also being choked. Speaking to the doctor, this is actually quite normal, which is why a lot of abusers go free....the woman doesn't remember all the details. It comes back to her more like flashes. But that was 25 years ago.
The second time, I faced down an intruder. I had a young son. Mothers do stupid things when protecting their children.
I didn't see him raise his fist. I didn't feel the hit. It was like I blinked, and suddenly I was sitting on the floor, wondering how I got there. No pain. Blood everywhere. The pain took about 30 minutes to make a connection with the brain. Then, I could hardly breathe.
Some people will feel the pain instantly, but for me, it was more like impact...but no pain. And then, like I said, the second time, I was hit so hard, I realized later that I must have been knocked out for a few seconds/minutes? Dunno. And I was in a sitting position, not lying down.
So, there you are. First hand account. Hope it helps with your writing.