Hi XXXXXXX~
It does sound like your pup is having a pretty severe reaction to the vaccines. The fact that he's 'slobbering' tells me that he's nauseated so it stands to reason that he wouldn't want to eat or drink anything if he's constantly feeling like he wants to vomit.
As long as his breathing is fine and he's not actively vomiting or having diarrhea at this point, I think allowing him to rest and relax is absolutely the way to go for tonight. If you have a kennel for him, now would be the time to put him in it and allow him to just 'be'. If he's still feeling poorly in the morning, then definately take him back in to his regular vet. They should, at the very least, be able to prescribe something like Reglan to get the nausea under control.
Of course, should he take a turn for the worse during the night, then do not hesitate to either get him to an emergency clinic in your area, or give your regular vet a call and see what they suggest.
I hope this helps.
Certified Veterinary Technician
Associates Degree in Veterinary Technology. State and Nationally certified.