Doctors are not government, but they are bound by a variety of government regulations (e.g., parent referenced HIPAA). I do trust my own physician, but he still has to report on me in certain cases or he will lose his license.

For big, uncertain queries I initiate I would rather find the answer privately and then decide how public do I want this info to be. Otherwise I am afraid that my options will be curtailed: "did both of your parents have heart problems? sorry, we cannot take you on that climbing trip", etc.