Great. Thanks for the additional information. I really appreciate it.
From your description, I can't help but wonder if your dog doesn't have the beginnings of something like Cognitive Dysfunction going on. Some middle aged or older dogs get a little anxious at night for reasons we really don't understand. At our clinic we refer to it as 'sundowning', where the animal is fine all day, but then becomes restless and agitated or fearful/anxious at night.
Some vets refer to it as geriatric cognitive dysfunction, and you can find more information here:
One thing you could do is talk to your vet about what they recommend for anxiety/dysfunction in dogs. I know there are some mainstream drugs that we often use such as Acepromazine or Clomicalm, and some dogs even respond well to something you can buy over-the-counter, like Melatonin.
Another option would be something to help with the anxiety that doesn't have to be ingested (eaten), so it wouldn't interfere with any other medictions they want to try. 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.