Ok... I got you.
But Multiple Personality Disorder, now termed as Dissociative Identity Disorder (DID) is not quite the same as schizophrenia although DID is still one form of mental disorder and needs treatment.
A definition of DID is as follows :
DID is characterized by a set of one or more distinct identities that a person believes to exist within themselves. These identities can talk to the person, and the person can answer back. The identities often are formed to help a person cope with different parts of their life, and seem to have distinct personalities that are unique and different than the person’s core personality.Treatment typically involves psychotherapy to help integrate all of the identities into the core personality and can take years when successful.
I have personally seen people with Bipolar Disorder and Dissociative Identity Disorder. They look normal and in fact,they can hold down a job. But under certain circumstances, I couldn't recognize the person with the BD and/or DID. They can change to another "person" who is hideous and scary and devoid of rationality.