A few people have asked today how he's doing, and the answer is he's just fine. He slept off the anesthetic yesterday (pictured) and today he's quite bright. We had a strong 40 minute walk in the spring sunshine.
We'll know more later in the week after his test results. I'm feeling pretty upbeat; at least Ollie's back is no worse, which was worrying me a lot.
UPDATE: The vet called Tuesday afternoon with good news that nothing was found from his spinal tap or blood tests, so major problems are ruled out. He's going to have one more simple blood test from his neighborhood vet for a potential vascular issue but Sooz and I have decided to chill out. We've done everything we can for him, and Ollie is still a happy dog. He's slower than he used to be, but Lord knows that's true of us as well.