Multiple personality disorder, i think i just had a revelation! your opinions, please.?

ok, here it is: i have always thought of mpd as being symptomatic in the extreme such as "Three Faces of Eve" and "Sybill," the movies; however, i'm now wondering if it's possible that most people (or at least some people) suffering from this problem might have more mild cases of it. example: someone who has been diagnosed as bipolar might in fact have the above mentioned diagnosis. maybe the drastic personality/mood swings are really symptoms of different personalities emerging. my estranged husband exhibits these characteristics....vacillating between hyper/egotistical/narcissism/delusions of grandeur to impatient, angry and paranoid to (when he's in sweet mode) talking baby talk and acting like a little child....referring to himself as "johnny," instead of john...ie; "johnny needs to go pee pee now."......all of this is seemingly done in joking, but who knows? we no longer live together. he was diagnosed recently as bipolar, but i'm starting to wonder if there is more to it.