Yup Sam thats pretty common and natural that usually because within your dream you somehow are displaying connections with your physical sleeping body. The slow motion or difficulty to display action in a dream is the result of you sensing your sleeping body. Things feel heavy because of the sleep paralysis that you are engagded in even though you don't feel the paralysis you can move in a normal free way like you could in the waking world. Enter the World of Lucidity and this will never be an obstructive factor for you.