I don't have any definite proof of this, but I've become fairly convinced that some dreams come along with a parallel dream memory. In other words, I can remember being in a dream and remembering what seemed like a long preceding event, but when I wake up and analyze the dream, it really looks like there was no preceding event in dream time -- just the memory of it which came more or less instantaneously. So the dream feels like it was longer than it really was.