just a small correction/clarification...
Actually, if you read the books carefully, it's more likely that Voldemort is bipolar, and that he is affecting harry's mood through the scar. This is lightly alluded to in the books, and all but out right confirmed in the OoP movie. Obviously, this doesn't work for your story, but i just though i should mention it to you. Actually, if you think about it, i think voldie has just about every single psychosis known to man! Autism, aspergers, and one hell of an oedipus complex, to name but a few!