This really happens to me! When I've been writing all day, for days straight and I go to bed thinking of my writing, I literally dream with images combined with a narration: "there appeared before me a living breathing woolly mammoth when moments ago I had been opening a can of spaghetti while riding a jet-ski over a sea of green lava..."
Sadly, the narration never adds anything to helping me make any sense of the dream. Lol