With my first I had already thrown up everything in my stomach long before I got to hospital. I had a shot of pethidine when I arrived about 8:30-9:00pm slept for a while, got back to the birthing suite abou 12am. I had gas only during the labour and DS was born at 1:37am. Afterwards, I went out for a ciggie (bad I know and won't being smoking this time). I was warned by the midwives that it could/would make me throw up and it sure did.
I think the biggest thing to remember is everyone handles drugs differently. The best thing you can do is have knowledge of each pain reliever so that when the time comes, you can listen to your body and be able to make an informed decision.
I had completely ruled out having an epi. I have slight hip dysplasia and although the doc's had said this wouldn't cause a problem, I knew that lying on my back was not an option. Because I know the issues I have with them, ie. what sets off the pain etc. I needed to be able to move around and deliver in some kind of upright position, so an epi wouldn't let me do that. I didn't know much about what to expect (good or bad) as I hadn't gone to any antenatal classes or done much research. I just went with the flow when it happened and I guess I was a lucky one.
This time around, I know a lot more about what I want and don't want. It makes it harder in a way, because pregancy and birth can only be planned so much. There are so many variables and unknown's. I like to plan and be prepared, but you can only think of so many plan B's.
I guess what I'm trying to say is prepare yourself with knowledge, have your ideas and ideals, but also know that not one thing could go the way you want, but that's ok.