Did you give your dog any medicine or did you bring him to the vets to get his shots..today or yesterday?
If he has been out side he might have been bitten by some kind of insect or a snake. Call your vet and tell them what's going on they could recommend something
My Daschund has had two allergic reaction to shots and had the same reactions...take him/her to the vet ASAP!! ...My dog almost died the second time. :(