My daughter is a nurse for a gastroenterologist, she says the vast majority of their patients are - from side effects from medications.

The recently "inherited" a bunch of patients from another Dr that died. In going over their charts there were quite a few who were being treated for "diseases" they didn't even have.  Worst one was a guy who can in at 20, Dr ordered a specific test that took a while to come back. In the meantime started treatment for that disease, guy came in once a week for 16 YEARS, for treatment. BTW the test came back negative, but no one bothered to look at the results, until she did.
They gut wasn't even upset when she told him.
ALWAYS question your DR