Ahh, iirc the two personalities can be aware of each other. There was one recorded case where the 'original' person would refer to the "bad" person, while the "bad" personality would talk about the "boring" person, although neither existed at the same time they knew of each other's existance, even having different names but I can't remember what they are now. Then of course some people might have the whole Fight Club thing going on too.