I think when you wake up from a dream like that, and either see or feel something in your room, your brain is still projecting those dream images in your mind. So you are actually seeing or feeling these things in real life, but they're only left over experiences from the dream.

Now, the scratches you described from the cat in the dream, Hypnagorama, I have no clue how to explain that. Either it was an actual paranormal experience, or you scratched yourself and thought it was the cat's claws. Interesting story, though.