A psychiatrist is doing his rounds with a couple of students. They look in on one patient, and the psychiatrist says to his students, "Sometimes this fellow thinks he's a temptress in a Bizet opera, but today, as you can see from his goose-stepping, he thinks he's the World War II head of the Luftwaffe. What condition do you think he's suffering from?"

The first student replies, "Is he a paranoid schizophrenic with a multiple-personality disorder?"

The second student says, "No, surely he just doesn't know ...

... whether he's Carmen or Goering."