Hello and thank you for requesting me. Given here age, I might look more to some type of canine cognitive dysfunction. Dogs that go through this can become more clingy, they can sleep more in the day and be up at night. They have anxiety in which they may do a lot of air licking. Usually it starts when the sun goes down, also known as sundowners.
Your vet really has no test for this, but will go on the oddities you see. Some dogs may forget other things, like what side of a door to go out of and others may stare at a wall or get stuck in corners. There are a variety of oddities.
What I would do is make a list of all changes and the time it starts. This will give you something to show your Vet.
Some dogs do well with over the counter melatonin given at night, but always talk to your Vet about any over the counter meds as your Vet knows your dogs history.
Melatonin dosing. Also make sure the melatonin you pick has not zylitol in it.