Some on this part of the forum forget it is not only for DID but all types of dissociation. Derealization and depresonalization are real dissociative diagnoses.

Of course thinking you are not really from here can be a sort of psychosis (delusion), BUT it can also be such a strong disconnect between what you KNOW and what you FEEL, that your mind will invent a story to explain this feeling of disconnect.

If you try to feel you are here, on your own planet, as a human, but the emotion of it is totally lacking because of dissociation, that can make a person need an explanation that might not be the correct one. The human brain wants to explain feelings so much, and other things too, to the point where it rather explains it wrong than don't explain at all.