In my fantasy story the MC's brother joins the war effort, but by the time the MC finds him again he's basically an axe crazy psycho. My reasoning is going to be that the brother saw and had to do so many horrible and traumatic things that he subconsciously created a personality that could deal with it, and thus that personality became detached, soon axe crazy. Does this have merit with actual split personality disorder, or is it something people are born with? And is it possible to reach the original personality? Also now that i think about it, how does one go about creating an entirely different personality anyway?