Bipolar (formerly known as manic-depressive) is a real malady. It has nothing to do with multiple personalities.
So is multiple personalities a real disorder or not?
I remmeber seeing a TV medical documentary once where a man would sneeze and change into another personality. And they caught it on-camera once and it really amazed me.
He looked, sounded, and acted like an entirely different person. And I dont mean in the little ways- like a person just acting differently , you would have sworn it was a different person.
His facial features were changed, his mannerisms, tone of voice, everything. I remember thinking that I if it was not real, it was the most amazing acting I ever saw.
I cannot recall any benefit to the guy at all. In fact, one personality was trying to stop the other from buying a car they could not afford.