"Disorientated" seems to be an accepted adjective! I can't imagine where I'd use it! To me, it has a stronger sense of the "implied passive." That is, "someone disoriented me, and therefore I have been disorientated. But personally, I'd never say it!
My AmHtg does not list "disorientate" as a verb. (Hence no past participle "disorientated.")