My dog won't stop hyperventilating an hour after we came back from a very short walk.?

She's a Belgian sheepdog who is almost 13 & she is slightly overweight (apx 5 lbs). I can't get her to drink any water. She is on antibiotics for a tooth abscess..It's also fairly warm in my house because theres no airconditioning. I don't know if teres really something wrong with her. I tried to pet her to calm her down & her heart rate is very fast. I'm just worried shes going to give herself a heart attack. Andy ideas what to do to help her calm down, or why shes like this?