What does a wrestler do if he or she is sore or in pain but has to perform anyway at a show?

They have special medical aids backstage. If a superstar or diva is sore they can get a massage in that area. There's even ice to be applied. Remember when Evan Bourne got RKO'd out of mid air from the top rope? Medical assistants were backstage with him and they were holding iced on his neck and trying to turn his neck sideways. If it's that serious, then they can forfeit or be replaced. Sometimes a superstar can come out of the ring and stretch, as in recover. Or during the middle of the match sometimes, they hold wherever is sore and leave the arena, and their opponent wins by count out. Cody Rhodes has done this before. There are also pain killers given, so I wouldn't worry too much.