Doctors, what are the odds of getting diseases/cancer from second hand smoke?

Low but not zero: compared to active smoking, the risks of second hand smoke are lower, but that depends on what quantity of smoke you are being exposed to. People in apt buildings can get very low levels of smoke through their vents and even through the walls, while waitresses and bartenders in places where smoking is prevalent may get very high doses. Reduce your exposure as much as possible.