Alternatively, simply don't make it a mental illness. A mental illness like DiD would be implied there's something wrong with you (and there may be). That being said, you don't need DiD to be a crazy person; let the coats label you however they want, fact is psychological science is tough to pin down since some people are just cray-cray without consistent facts or cures.

Though I'd also take into account a willing suspension of disbelief when it comes to emulating real life dieseases the same way I would with skills: just because you lack the knowledge or experience of the subject matter doesn't bar you from attempting to emulate it. You'll be wrong, likely, but that implies there's a "Correct" way to say, be mentally disturbed.