Apparently, when attempting to diagnose appendicitis, some doctors would ask if pain worsened when driving over speed bumps. It was not exact medicine, but according to Dr. Helen Ashdown of Oxford, it has been "as good as many other ways of assessing people with suspected appendicitis."
The Oxford study showed that the speed bump test was more helpful at ruling out appendicitis than confirming its diagnosis since other abdominal issues could also cause pain in those situations. So patients with acute appendicitis would experience pain going over a speed bump, but those who don't feel a jolt can be ruled out entirely as having acute appendicitis. That said, don't go driving over speed bumps expecting to perform your own diagnosis. Your results may vary!