A patient describes sometimes acting or speaking in a way that feels automatic, as though driven by another part of herself, while readily acknowledging that this is just how it feels, not a literal belief that she is genuinely two separate people. Before revealing the answer: is this the experience of multiple personalities?

No, this is more consistent with a disturbance of self-unity than with the experience of multiple personalities. The experience of multiple personalities involves genuinely distinct, separately characterised personalities, often without qualification; here, the retained 'as if' insight and the absence of genuinely distinct, separately named personalities is the defining pattern of a milder disturbance of self-unity rather than the more severe, specific experience of multiple personalities.