This could be a serious spinal issue — you need to take him to a vet for evaluation. Swelling disks, a pinched nerve, could be the problem, but you can’t be sure what is going on without a vet’s evaluation and probably an xray or soft-tissue scan. Any thing involving the spine is pretty serious in my book, so I wouldn’t wait. Often problems can be resolved with crate rest and some medication for swelling and pain.
Good luck!
i’d guess this is a dental issue. can you check his mouth to see if he’s broken a tooth or maybe has something stuck?
Drooling can occur for a number of reasons. Yes, dental issue is certainly one of them along with a foreign body in the mouth, licking something disagreeable or upset stomach. Either way, something is amiss. Unless you can safely check for something lodged on that side of the mouth, or don’t find anything, and it doesn’t go away by tonight, do have it checked.
http://dawgbusiness.blogspot.ca/2012/04/symptoms-to-watch-for-in-your-dog.html