Answer: We don’t know why we are sick because we don’t see the entire system of creation. Someone does something in one place and for that someone in another place “takes it on the head” because we are a single integral system. So I cannot tell you how to act when someone is sick.
We need only to advance towards an inclusive unity. Only this alone! As Baal HaSulam writes, love of friends is ready to cover all of our problems.