These stories have a similar theme, but don't match the basic premise.

Inverse situation, or simple indifference.
That is, the ex-human has memories of being human, states such, but doesn't really believe that they are real memories.
Or, a local got polymorphed, but nopony believes that they were, and that their new form was always the correct one.
Or, something else that could be considered close but not a match.