I have fallen backwards in a dream trying a new flying technique and to my complete surprise, instead of floating like I was convinced would be the logical result to my action, I hit the back of my head against the hard ground and it hurt. But then the dream continued and there was never a time where the pain was unbearable. I think the difference between pain in dreams and in real life is that pain in real life is unbearable because it stays. My advice is pain shouldn't be a deterrent for you. It really is not the same as pain in real life, even past the fact that there is no harm actually being done.