Lewis seems to talk a lot about pain and loss. As you know, he has two books clearly on the subject, The Problem of Pain and A Grief Observed. We may throw in The Great Divorce and The Screwtape Letters if we widen the thought of explaining pain with the reality of death and the struggle of this life.
Lewis never attends to an easy answer. He's not confident in that. Instead, he quotes Augustine: "God wants to give us something, but cannot, because our hands are full - there's nowhere for Him to put it." So, what does God do, according to Lewis?
"While what we call 'our own life' remains agreeable we will not surrender it to Him. What then can God do in our interests but make 'our own life' less agreeable to us, and take away the plausible source of false happiness?" So a heart attack or pancreatic cancer or the loss of a job or the loss of something even more grievous, like a wife in Lewis's case, is all to hunt us down and break us open for the Gospel. Lewis knows it's not pretty nor what the ruling reasoned class would have, but if our run is rooted in the love of Jesus, we must trust him.