I have taken Human Physiology, then Anatomy, then retook Human Physiology, and I have also taken A&P I&II (long story).
I recommend taking Anatomy first. I took Physiology straight out of my intro Bio classes and barely passed. You need a little rudimentary knowledge of anatomy to fully comprehend physiology and I had nil. I felt I spent half my time learning basic anatomy while my upper level classmates and grad students already knew it and could get down into the physiology right off the bat. I retook physiology after I aced anatomy and it was a hell of a lot better. Both because I knew the anatomy and because it was my second time around. I don't feel prior knowledge of physiology helped me in anatomy as much as it did the other way around.
I agree that if they are challenging classes like dontlikephysics' and mine were, taking them together will be hell. Anatomy is very time consuming.
However if they are sophomore level classes, it can be quite nice to learn the material together. I took our school's A&P which is more for nursing students, and was something like a joke--especially after I took all those upper level courses. I just took it because I was paranoid my "3 hour anatomy with a lab" did not qualify for schools that require a "4 hour anatomy with a lab." Now I know that it does count after all, but oh well. GPA booster and now I am VERY comfortable with both subjects. Good luck!
