I'm so sorry for your loss. RIP Dear One.
I don't know where you live ut last summer during tick season my APBT showed the same signs he acted as tho he was drunk he couldn't walk he couldn't stand up he fell down the stairs. He had been bitten by a tick carrying Erlocious(sp?) it affects the nervous system. There were others in the area a few died because he owner didn't get their pet to the vet quick enough. I had Mikado there the next morning as he showed the first signs at 10 the night before. I hope you find out what happened to your baby.
I too believe that we over vaccinate. My vet doesn't do yearly vaccs.