A story I heard from an attending physician:
Back when he was an intern, there was an ICU nurse who began having fevers, weight loss, and was coughing up blood. Being a nurse, she diagnosed herself with lung cancer. Since there was no effective cure, she decided not to seek medical attention and continued to work at her job until the end of her life, which she assumed would be imminent. About six months later, she died as expected.
Shortly after her death, my attending (then an intern) received a letter that explained that an ICU nurse had recently died of disseminated tuberculosis and they were contacting everyone who had worked with her to tell them to get a PPD. Apparently, she had misdiagnosed herself. Not only did she have a disease that was treatable and her life could have been saved, but she also managed to spread TB germs to all the really sick ICU patients she worked with.
"... and that's how I converted my PPD."