Earlier quoted context omitted.
Contrary to popular belief, schizophrenia is not the same thing as dissociative identity disorder/multiple personality disorder. (Which is I believe what you were suggesting with that joke.) From Wikipedia: Schizophrenia is a mental disorder characterized by a disintegration of the process of thinking and of emotional responsiveness. It most commonly manifests as auditory hallucinations, paranoid or bizarre delusions…
"dissociative identity disorder/multiple personality disorder" has been all but dropped by mainstream psychology. It's considered to be an artifact explained as being induced by a number of factors including attention seeking, desire to please therapist, extreme hypochondria and mimicry.
As with many mental illnesses, whether or not it's real depends on what your definition of 'real' is. It's clearly a common pattern of behavior that's secondary to other factors, but you could say the same thing about lots of mental illnesses.