The Concept of Tikun
There is a spiritual concept of "tikun" that gives us a perspective conducive for serenity. Kabbalistically the term "tikun" means "rectification." Difficult and distressful life situations serve as a rectification for one's soul. A person accepts, and is even grateful for, medical treatment that heals and cures even though it can be painful. So, too, knowing that the challenges one faces serve as a benefit for one's eternal soul, makes it easier to maintain serenity when facing difficulties.