It’s amusing when Dad falls asleep after Xmas lunch, but digesting that fantastic meal takes a lot of effort. Simply, digesting takes a surprising amount of bodily energy, and if a meal’s very large or complex, the rest of the body has to close down to allow for it. That’s maybe ok now and again for a healthy person, but if you have a serious health problem, especially cancer, every bit of enzyme activity is needed for the immune system to fight the disease, detox, process the drugs, and repair cell damage. (More on this another time). Digestion takes more work for all of us as we age anyway. (It’s usually only the kids who are left standing)
So maybe stop before the pudding stage? Take them all out for a walk and a kick around, and come back for pudding later? Have a happy healthy lovely family day.