I had one at 36 weeks. It wasn't painful, just uncomfortable - they lay you down but tipped slightly so your feet are higher than your head. That and lying on your back with all that weight is interesting. Then they give you ventalin via IV to soften your uterus for the massage, and the ventalin makes your heart race. So that is what I was unprepared for, I ended up getting oxygen via a mask to calm me down, and then needed a cool flannel for my forehead afterwards. Not that I want to scare you, it's just things I wished I'd been prepared for. But the actual massage to turn the baby was fine, and happened quite quickly and easily, and my bubs was frank breech.

I also don't know if my reaction was stronger because you have to fast for a few hours beforehand, and I had GD so my sugar levels dropped quite low.