Great. Thanks for the additional information. I really appreciate it.
So if this were me, I'd actually have your vet give him another physical. I'd ask them to do some thyroid testing. The reason I say that is because thyroid problems can often present initially with changes in mentation...meaning, changes in behavior.
If that comes back clear, then you may want to ask your vet if he thinks this could be something like canine cognitive dysfunction...this is pretty common in older dogs. You can find more information here:
Something you could consider would be talking to your vet about a light sedative for your pup. One that we use is called Clomicalm and really seems to work well. Of course, you'll have to talk to your vet to make sure that this is a good option to use with your boy.
Another option would be something to help with the anxiety that doesn't have to be ingested....I love using the DAP collar:
These are collars that are impregnated with a man-made version of the dog appeasing pheromone, which is a pheromone that nursing bitches give off to their pups to help them feel calm and secure. It's something that humans can't smell, but it has an amazing effect on dogs with anxiety and other issues. Although you can find them at your vet's office..you can also find them online at places like Amazon.com and Ebay for much cheaper. Just make sure they're DAP brand, as they seem to work better than some other versions.
I've used the DAP collar in my own dogs and with some of the dogs I've rehabilitated and I really, really like the results. Just keep in mind that the collar only lasts for 30 days, so you'll have to replace it monthly if it works for you.
I hope this helps.