Multiple Personality Disorder is not a form of schizophrenia, or vice versa, as many people seem to believe. Schizophrenia is detachment from reality, while MPD is the condition of having at least two very real personalities.
As MPD is a type of Dissociative Disorder. Often a personality may be unaware of the other(s) it shares a body with, although in some cases the personalities do talk to each other. MPD may sometimes accompanied by intense headaches and extrasensory experiences.
Nearly all sufferers of MPD have been abused, either sexually of physically, as children.