Hello, I am so sorry to hear about Shadow. 20 is very old for a cat; I have never been lucky enough to have a cat live this long. You must have given him a good life. My name is Rebecca. I am a veterinarian and will do my best to help. If he has stopped eating and drinking, he is probably dying, and at his age, he is probably dying of something we can't treat or cure, such as kidney
disease, heart disease, cancer, etc. Cats when they get chronic diseases like kidney disease and cancer are so good at hiding their symptoms and that they don't feel good can often be sick for weeks or longer before they owner even realizes anything is wrong. I have seen cancer present as an "emergency" over and over again. The only way to know for sure what is wrong, and if there is any treatment, would be an exam by a vet, and possibly things like Xrays or blood tests. I can understand your wanting to spare him going through all that. I have seen cats like this, even if they are not eating or drinking, take days to pass away and that can be sad and hard to watch. I have had many clients bring a cat like this to me for euthanasia after not being able to bear watching them any longer. However, he may pass peacefully on his own soon. Do you have any house call veterinarians in your area? That is an option, to have a vet come to you, give a quick injection that causes sedation, and then when he is asleep and unaware, giving the final intravenous injection to help him pass. I often do housecalls for my clients, and some veterinarians do only housecalls. Let me know how he is doing and what other questions I can answer.