it didn't have to even be a conscious decision on the part of Chuck.
with all we know about science and medicine, there is still a very large and real % of healing that is a mystery and intertwined with the intangibles contained within a patient and their circumstances.
I could see how the Colt's season, gave Chuck extra motivation, hope, energy, and positive feelings (which come from positive healing neurotransmitters/hormones ect) this all contributed to Chuck getting healthy in time to come back. Hell the cognitive dissonance from his post game speech after a victory about dancing with his daughters at his wedding and winning super bowl rings, might have been enough.
If the Colts were 4-11 entering yesterdays game, Chuck might still have been literally too weak to get out of his hospital bed.