This is very often a SEVERE reaction to something. You should get your dog to the vet as soon as possible as without intervention it can result in death (and sometimes VERY quickly) on occasion if that's what is going on. You also may want to try and figure out WHAT your dog could be reacting to so as to limit exposure or to be better prepared next time. Did your pet receive vaccines today? What about getting stung by a bee or bit by something else? I hope everything turns out well for both of you.
