I need help! My oldest cat, Shadow, was outside with me earlier today when I was grilling dinner and a stray cat, who he has socialized with before with no problems, came around and starting howling and hissing at him. No fight occurred, because Shadow was immediately ordered back inside and I kept the female away from chasing him (she initiated the problem).

It has now been almost 6 hours since the altercation and Shadow is still hissing & growling & attacking the other inside cats. I've given him some meds to try to calm him down but they haven't worked. I've currently got him separated from the others to give him some alone time to calm down, but I need advice on what else I can do to help him!
When I've been laying in bed resting with him this evening, he'll lay curled against me, with his head buried into my arm. If I could be sure that the other cats wouldn't come near us, and that he'd stay, I'd let him stay there all night to comfort him, but I can't guarantee that he would stay there.

Please ANY suggestions and advice would be greatly appreciated!!
Just keep him away from the other cats until he's calmed down completely. Nothing else to do.