Probably good to talk it out. Maybe you should knock back something to help sleep tonight.
Not near as tragic, but I've run into the CPR vice Neck injury quandry before. As an Ice hockey coach I had a player knocked out head-first into the boards. I was the first adult to him and he was face down with a helmet on and not apparently breathing. I felt I had to move him to establish an airway as that was the more important problem at the moment. As I rolled him over he spasmed and started breathing on his own (very reminiscent of when Paul Kariya was knocked out by a hit in the playoffs a couple of years ago). He got away with a concussion and an afternoon in the hospital.
I'm no doctor, but I think if someone's not breathing they could be dead in 6-9 minutes so neck and back injuries must take a back seat for the moment. Not that you can't try to minimize vertebrae movement as you establish an airway. I'd never considered this before it happened to me. Maybe someone with a real medical background could comment.
In your case, I don't think it would have mattered what you did. Sorry you had to be in that position. Many people wouldn't have even gotten out of their car.