Good to know and ask our vet about if this becomes a chronic issue.
I have thought that something latent surfaced, his immune system maybe dropped, so then the concern is why, could something else more serious be developing, etc.
Happy to report that he is improving! He has sneezed a few times today, but he is talking again and his voice sounds better. He can eat and drink without coughing now, it was putting him off. He got up a few times today and walked around the house, he asked to go outside to sit on the deck for five minutes three separate times, once when the chickens were there too, and he just got up again to spend the evening with DH watching TV. This is a great improvement from the last several days of almost continuous deep sleeping in his quiet nap bed.