These are one of the funniest kind of jokes because the Medical profession is otherwise a serious profession.
John and David were both patients in a Mental hospital. One day, John suddenly dived into the deep end of the swimming pool. David jumped in and saved him, and the medical director came to know of his heroic act.. The doctor immediately order David to be discharged from the Mental Hospital as he is OK.

Doctor: We have good news and bad news for you, David. The good news is that we are going to discharge you because you have regained your senses,since you are able to jump in and save another patient you are now a normal person. The bad news is that, the patient Mr. John, whom you have saved, hung himself in the toilet, and died. David: Doctor, he didn't hang himself. I hung him there to dry!