Look, the absolute best thing to do is get the cat to the vet ASAP. But the truth is, it's the weekend, and if you are in the Western Hemisphere, it's night time. So the question is, is it really necessary to take the cat to an ultra-expensive Emergency Clinic? Well, it would be great if you could, but in your shoes, I would try to call and have my own vet. paged to ask about it. If it is a wasp sting, the vet might be able to help you figure that out with more certainty over the phone. And if so, might advise something like administering benedryl - but you MUST have a qualified vet tell you the proper dosage, or risk a potentially fatal overdose. The cat is eating ok, and breathing ok? And acting pretty much as he usually does? Those are signs that it _might_ be ok to hold off until regular office hours at your vet's.