It seems like the main difference has to do with what causes the change in mood - are you reacting to the world (in an 'abnormal' way) or is your brain just free-styling? But it's really confusing because sometimes it's hard to tell the difference. For example, I may totally overreact to something that happens to me either because I have a personality disorder, or because I'm in a (bipolar) mood that makes me more sensitive/upset/irritable in that moment. And if you're ultra-rapid cycling, how do you really know if the mood or the trigger came first?