There's only one way to get to the bottom of Sam's problem and that is a blood test. When I saw your title line, I immediately thought hyperactive thyroid, but it could be any number of things.
I do not know why you can't give him a small dose of tranquilizer before you leave the house so that when you get to the vet he'll be more relaxed. The two of you could share a tab
I can see how an anaesthetic would be overkill but how can a mild tranquilizer throw off a test? Maybe Dr. Lee will see this.
Try not to worry until you have to. Many of these chronic, late-onset conditions can be controlled, if not cured.
But if overall your vet is not as skilful as you'd like, find another one.