The only difference between standing up and being counted as one of these other things and standing up and being counted as a Multiple is that it takes a little longer. And some would uncharitably suggest that the result is an irrational number. What Multiplicity Is I'm a Multiple. Dissociation is a spectrum, and most people are somewhere along that line. Most everyone has the ability to disassociate at need, whether in combat or changing the litter box.
Some personalities are more developed than others.
Very often there are specialised personalities for dealing with particular situations, such as sex, public speaking, partying, or driving. Some handle stress better than others. Some are better at remembering things than others. It's usual for different alters to remember different people and things. Finally, Multiplicity is not insanity.