illness
In the US, doctors cannot share personal health information (PHI) without consent.
However, in some circumstances, a patient can be involuntarily committed for treatment. It's an extreme step, usually warranted only when the patient is a danger to himself or others. Obviously, this would have a negative impact on the person's career.
There should be a middle ground. How would people feel if doctors were allowed to convey to the airline a pilot's fitness for duty without specifying the exact reason?