A common sensation amongst cosplayers in which they cosplay a character, and said character develops an alternate persona in their head. The character does not take over their consciousness, but often comments on their lives, and can sometimes influence them to do somethin (or else character will complain. relentlessly.) Can be likened to a very annoying, but tolerable alter-ego.
This is also a common ailment for writers and online roleplayers as well.
Person 1: Since when did you start drinking Earl Grey Tea every morning?
Person 2: My inner (character) wanted it.
Person 1: Looks like you have Cosplay Personality Disorder.