Please do not dismiss this is a minor event that might have been due to a tickbite. If it was caused by a tick, it was certainly a very worrying reaction. Fingers crossed that may be all it was.
But please do not start to soften what you yourself saw and recorded -- this is how many dogs with serious conditions get left to deal with a serious probem without any pain relief while owners try to convince themselves what they saw wasn;t as bad as they initially remembered.
The fact that he has improved may well mean whatever he has comes and goes, not that it was a once off -- you were describing a very serious pain or seizure session of some sort. It does fit with what often happens with syringomyelia, from the neck stiffness and pain to the wandering eye to the shivering and the limb weakness. Such sessions come and go with SM as many of us, including Cathy Moon who had the very severely afflicted Charlie, can tell you. You must take this seriously. Most likely last night they gave him pain relief and all the usual sorts of pain relief from basics like aspirin and metacam to steroids can halt an SM pain session or a session caused by another serious problem, and may give days or even weeks of relief. That does not mean the problem isn't there. The same with back pain -- though the symptoms you saw really do not fit disk pain, which doesn't usually cause a wandering eye for example. SM can; it can affect the optic nerve.
It sounds like you had a very good vet who will proceed with the right array of tests. If you see a repeat of this type of pain session I am sure he will probably advise getting an MRI if nothing else is found.
I would consider too that this may well be why these dogs were originally handed in to rescue. Many owners would see one such event as this, know something was potentially seriously wrong with the dog, and unload to a new home. sadly we see it all the time with MVD dogs and Charlie came from exactly such a situation, abandoned at a vets because the owner realised he had SM.
Please stick with your vet through this and take what you saw very seriously. Or to put it another way -- if one of your children had presented these symptoms, the combination would deeply worry a parent. You saw a very alarming set of symptoms that indicated severe pain and possibly some sort of seizure. Please do continue as you are with a proper investigation for Noodles' sake.
