Inability-to-Run Dream

This is a very frustrating dream. I want to run, but can't. It doesn't matter if someone is chasing me or I just want to go somewhere fast, I can't run. When you run, you need to lean forwards. Therefore, in the dream, I try to lean forwards, but can't. Something is almost pushing me backwards. In the dream, I have even reasoned that if I can't run forwards or lean forwards, then why not lean backwards and run backwards? That way, at least, I can get moving. What happens is that I can't lean backwards either, and my feet are immobilized and I don't make much progress forwards or backwards. When running, you need to first bring your knees forward and up so that you can kick backwards, but I can't do that either. What would cause such a sensation while I am sleeping? I discovered the cause of this dream after I had solved the falling dream, so the explanation was easier to find. Again, the explanation came to me when I awoke immediately after the dream and found myself sleeping face down, on my stomach. Eureeeka! When lying on your stomach, you cannot change the angle of your body with respect to the bed; you can't lean forwards. Can't bring the knees up either, because the bed is in the way. Can't lean backwards because gravity is pushing you down. Can't walk backwards because the bed is in the way. This demonstrates again that you don't have much control over your muscles while asleep because, if you were awake, pulling the knees up wouldn't be that difficult even when lying face down. After finding the explanation, I was again able to verify it several times; i.e., when I awoke, I was sleeping face down. At this point, I began to realize that maybe, most of my dreams had a physical explanation. However, the whole thing didn't quite make sense, because -- why would my brain not know that my knees are dropping or that I am sleeping face down? How can my brain dream such a complex dream and yet not be able to figure out such simple things? And again, my brain has concocted a false situation and succeeded in making me believe it while dreaming.