Hi Simon,
My boss has been battling cancer for the best part of ten years - he goes in and out with his medical, but still flies as much as possible.
Take your energy, beat the cancer (think Lance Armstrong), then take some more energy and beat the medical.
Sometimes you don't KNOW the reason until much later, but everything happens for a reason - go with that and your journey will be much easier!
From across the pond, fair winds!