Hey Nonie, (as usual) I'm seconding what Cat said, you can't forget your body's hormones (Cat I was up til about then with a 1:30pm birth!!)

I went in wanting a natural waterbirth, and my 2 birth support partners (dh and midwife student/mate) knowing I wanted a natural waterbirth. I always said I wouldn't be too proud and stubborn and if my partners could see that I wasn't coping then I knew I could trust them to advise me to have something to help me cope.
I totally wasn't prepared for, and didn't count on, those labour hormones kicking in. The put me into a 'zone' where I was totally focussed, gave me energy, and though it hurt, I could handle it with the encouragement and support of my partners.
So i got my drug free waterbirth!

Besides, what did all those women do before drugs were available? The human race has been alive and kicking for slightly more than 50 years
You can do it. My advice would be to have a birth partner/s who believe the same thing.

All the best, and congrats on your pregnancy! Sept's a great time to have a baby