Dissociative Identity Disorder

We learned about dissociative identity disorder this week. We defined it as previously known as multiple personality disorder - having 2 more distinct identities that control the person's behavior. We talked about how it's very controversial, similar to how hypnosis was.

I read an article (sorry Rachel, I know that's your thing) about whether or not dissociative identity disorder is real or not. Someone asked the question we did "is it real or not?" A mental health expert, Dr. Charles Raison, answered the question.

He first summed up the opinion of those who are opposed to it: they think that the condition doesn't exist, or that if it is, it's 'iatrogenic' -- it's caused by therapists training their patients to interpret their symptoms as if they have a whole set of distinct personalities.

Then he tells about those who agree with it: therapists will hold separate meetings with each of the patients other personalities (how weird?).

He then tells his own opinion: he says "The dictionary defines dissociation as "an unexpected partial or complete disruption of the normal integration of a person's conscious or psychological functioning that cannot be easily explained by the person." I don't think anyone could doubt that this phenomenon exists." 
He hold up his claim by saying that dissociation is when you're doing something important, then you lose track of the part of yourself that's doing it.  He says that he doesn't believe that they're actually present, but that they are convinced that this is actually happening.  

It's a weird concept - that a single person could have multiple personalities in their head. It's hard to imagine as well. I would like to think that dissociation to this degree is impossible and that dissociative identity disorder doesn't exist. What do you think?