FWIW....(not to doubt Riley) dissociation is not a personality disorder. Dissociation is the name given to a symptom: disconnecting from one's thoughts, feelings, memories or sense of identity....usually triggered by anxiety/trauma. This symptom can appear in Dissociative Identity Disorder (used to be called Multiple Personality Disorder), Dissociative Amnesia and Depersonalization/Derealization Disorder. Those three disorders are not considered personality disorders, and for reasons too involved to mention here... there is no longer a classification for a Personality Disorder based on Dissociation. Dissociation (the symptom, not the "disorder") can be seen in several psychological conditions.
just my $0.02