Stroke in canine is known as geriatric vestibular syndrome and is either a problem in the brain, or in the inner or middle ear. It can be due to inner or middle ear infection a small percentage of the time, the rest of the time the problem is due to unknown age related disease. The symptoms of this disease include, circling when trying to walk, falling down, a head tilt to one side, wobbliness, nausea and vomiting, inappetance, and an eye problem called nystagmus, and more. If your dog has a very mild version of "stroke" he could present with the problems you describe.
If he has a brain mass, or lesion in his spine (disk disease), he could have the kinds of symptoms you describe. Disk disease can be caused by extrusion of disk material, or a tumor, which presses against the spinal cord, and causes pain and neurological deficits.
Very often, blood work and other diagnostics are normal for vestibular disease or disk diseases. To find a brain or spinal lesion a CT Scan or MRI is usually necessary. A veterinary neurologist can perform a neurological exam which may be able to locate the lesion. If your dog has disk disease, steroids, acupuncture, and possibly surgery may be necessary. There are also some excellent Chinese formula's which can help for disk disease or vestibular disease, but require a definitive diagnosis for a successful treatment.
If your vet does not have a definitive diagnosis by the time this is posted perhaps you should ask your vet for a referral to a veterinary neurologist.
This sounds like a disk problem to me. Did your Vet mention anything pertaining to the back or neck? IMO, shaking IS a sign of pain. Gook luck, I hope he gets better, soon. The Vet (Here), will have some good answers for you. She will probably respond tomorrow. I just wanted to share my thoughts on this....Karla