Hi Otis, and welcome to SpiritKeep! =)
Dogs and cats, and other animals, are sensitive to spirit activity. People who are deaf or blind develop extra keen perception in their other senses to compensate for the loss of one of the primary ways of interacting with the world around them. I think that it is probably no different in animals. Perhaps the dog had a 'feeling' that something was there, or was awakened by a spirit touching him, or disturbing him in some physical way. I know that this physical touch by spirits is possible, because I have experienced it on more than one occasion.
One of these 'touching' experiences was witnessed by my adult daughter. We were sitting side by side at our computers. She was looking over at me and we were talking. A ghost grabbed the lower back edge of my blouse and yanked it downward sharply. She saw my blouse move in an unusual way, a way that could not have been something I did. It was a cropped blouse tied in front under the bustline. The blouse flattened against my spine when it was pulled downward, also moving the shoulder areas of the blouse. My hands and arms were still at the time. We just looked at each other, wide-eyed, because we had also noticed a shadow ghost near my shoulder. I felt him there, and we both looked back when my blouse was yanked, and saw a dark shadowy entity behind and above my right shoulder. My daughter saw him too.
Our dog, who is a healthy 4 year old beagle, and has his sight and hearing, has had an encounter of some sort several times on our living room couch. He reacts so strangely, we are at a loss to explain what it might be, other than spirit activity that causes him to do this. He will be sleeping, or sometimes just sitting on the couch. He lets out a small yip, dashes off the couch with his tail between his legs, and runs to the front door and digs frantically at the tile floor, as if digging for something. We can't get him to stop. Or, he will sometimes go into the kitchen and into a pantry area, and dig frantically at the floor there. He is oblivious to any efforts by any of us to get him to stop. Afterward, he acts frightened of getting on the couch for quite a while, and then we can finally, after lots of coaxing, get him back up there to lay down. It is a leather couch that we bought new about 10 years ago, so it shouldn't have anything 'ghostly' connected to it from previous owners.
So, I do believe, Otis, that your deaf dog probably did have an encounter involving senses other than hearing. Some of the dark shadow entities have a peculiar odor, and maybe he picked that up, or perhaps the spirit just poked him, and he was able to see or sense where the entity was (near the chair), or where it had disappeared..... Has this happened more than once? If so, you might want to keep a loaded camera near your bedside, and take some pictures if it happens again. One of those disposable cameras would work quite well for this, as it wouldn't tie up another camera for this purpose. The disposable cameras seem to do quite well in spirit photography.
I am looking forward to hearing about your experiences with your ghost who has been around for some time. Several of us have 'resident ghosts' in our homes, too.