You're not thinking logically enough within your dreams. One must only realize that every object, character, and physical law within a dream is merely a construct of your mind, mere electrical signals interpreted as images. As such, at the very base of things, there are no physical laws in dreams because none of the objects "exist" as matter created from atoms nor is they’re truly any large body to cause a gravitational field. There are no laws.

I suppose that this statement is somewhat similar to a quote from the Matrix. “There is no spoon. Then you’ll realize that it is not the spoon that bends, it is only yourself.”