Schizophrenia usually deals more with hallucinations and cognitive issues than jumps in personas. You're maybe looking at multiple personalities?
If Wikipedia can be trusted to give me the right symptoms for both, then Schizophrenia could be right as sufferers can hear voices. I wanted him to hear voices that sometimes scared him, making him shy and anti-social and very easily spooked. But sometimes listening to the voices would give him confidence in his magic to cause harm to others.
