Mr. Legion is both insane and sane at the same time. In his opinion, he is sane, while his hallucinations are not. Yeah, hallucinations, really cool hallucinations.
Legion is a novella by Brandon Sanderson. I downloaded the audiobook for free on audible.com, and you can to. The characters and premise are brilliant. The plot could be a bit better, but Brandon discovery wrote it on a plane, so I'll cut him some slack.
Go check it out!