Chester has had bad reactions to his vac, but one year in particular he had a very bad time of it. He was very lethargic and wouldn't eat or drink for about 24 hours. He barely moved from one spot, and looked very scared and pitiful. I do feel the vacs are worth it, though and so we get them every year. That was the worst reaction he's ever had, but each spring when it's that time again, I worry. I'm sure Snoop will be fine. Give him a day or two to recover. If he's not back to his old self, I'd visit another vet.
I'm with binka_nugget, I usually try to wait it out, rather than medicate.