Now it's possible neither of those things can actually exist, but the fact that I can imagine them demonstrates the distinction I'm making.
Hmm, really? How? To be honest, I can't. Honestly I think this is just a meaningless mind trick. The more I think about it, the less the notion of a p-zombie really makes sense to me. If a p-zombie existed, and I could never really tell the difference from the outside, this gives rise to many blind-alley-models of the world, for example solipsism: Maybe all others are just p-zombies and maybe I'm the only thing that really exists in the sphere of consciousness (=soul?). I can never know for sure. But if it's true, then there's not really much room for any further discussion.
So I have to assume that everything that behaves like being conscious in fact has a consciousness - even if it isn't even aware of its being conscious.
And the point isn't whether such a thing is physically possible in our universe, merely that being able to conceive of such a thing identifies the distinction we're drawing. There is a notion of experience separate from the physical process that may cause it, because for any such process, we can imagine a world where it does not actually experience anything.