please help

I don’t understand what is wrong with my cat. My mom is on the way home so we can go to the vet but I don’t understand if this is an issue we CAN’T wait for, yknow? Yesterday, he was really fussy and when I tried to stand up while he was laying on me, he hissed. Now his face is swollen, he looks like a beluga whale. Please, he usually gets into fights outside but it’s never been this bad. I keep begging everyone to let him stay inside, they don’t listen to me.