Each Alternate Personality in Multiple Personality is an Unreliable Narrator, Because Each One Has a Magical, Idiosyncratic, Partial View of Reality

In multiple personality, each identity has it own reality in regard to self-image, memories, interests, and world view. Each identity’s self-image—as to appearance, age, and even sex—may be quite different from how they appear to you. Each identity’s memories may have gaps, and each identity’s interests will lead it to attend to certain things only. So each identity’s overall view of reality will be distorted accordingly.

Thus, if a character is an unreliable narrator—and if the unreliability cannot be completely explained by ordinary common sense—then you should consider multiple personality.

What about drugs and alcohol? Couldn’t memory gaps be caused by alcohol blackouts? Possibly. But are you sure that the character has never had a memory gap when not drinking? And even if you could be sure that they never have, are you sure that the character does not have an alcoholic alternate personality? Are the story or character more peculiar than you would expect from alcoholism alone?

In short, consider the possibility of multiple personality whenever confronted with an unreliable narrator—especially if the narrator is inclined to idiosyncratic, magical thinking—because that is the nature of alternate personalities.