It is possible to self-diagnose high functioning anxiety, but it is a difficult task to do. One functions normally and even better than most of the others at the workplace and professionally. There is almost no reason to believe that you are suffering from any sort of disorder when you excel at the workplace and elsewhere, but the truth is that high functioning anxiety is something that is completely internal, and not many will be able to see it or self diagnose it as it is blurred by the successful side of one's life.