Hi Tropical Horizon and Welcome.

Sure I have some idea on what you are experiencing. Now if you all could back me up on this.. ladies and gents.

I know that when you are sleeping your body shuts down for a brief period of time, this happens so you would not act out any of your dream responses during sleep. Sometimes in your dreams you still feel the connection with your body while its sleeping The inability to run is exactly what it is your legs during sleep becomes heavy and cumbersome due to this breif shut down period sometimes during sleep you cannot move your legs or other parts of your body, this may have some effect on your dreams because while you are dreaming you are still somewhat feeling your body (which happens sometimes). This experience is nothing to fear for it is normal everyone bodys shut down during sleep. I believe in any given time of your dream where you feel the need to run is usually because you're running away from something that causes fear within you, and whenever your feelings become aroused by excitement or frear sometimes it may spark things within allowing yourself to become active this is the early indication of feeling your body begining to wake from the dream. Noticed whenever you have a disturbing dream you wake up abrubtly and sit straight up in your bed like something just jolted electrical voltage within you. This is your body reacting once again. So this is what you are experiencing and its normal so don't fret.