However, what the person sees in the dream is nothing but the product of his imagination, and accordingly, the laws that would apply to the actual objects if they were seen by the physical eye in waking life do not apply to the images seen in the dream. The dreamer may dream that he sees a certain thing, yet that very thing may turn into something else in the same dream. These changes do not occur in such a way that the person can actually see the transition from one to another in the way the physical eye would see the transition if it took place in front of the person. In the dream, the person sees what he sees in one way, then afterwards he sees it in a different way. You cannot object that it was not that way a moment ago, for this is simply the way the imagination works.
What the Imagination Creates in Prophetic Dreams
Kalach Pitchei Chokhmah 8:8