人格分裂 ~= split personality
雙重人格 ~= multiple personalities
I'm not a psychologist, so I can't really tell you the clinical difference between the two terms. I'm just giving the translation. After reading a few articles, it seems that there is very little clinical difference between a split personality disorder and a multiple personality disorder. They are both referred to as "dissociative disorders", the new fancy term for these things.
疑神疑鬼 ~= extremely suspicious