"I don' want it." Joel muttered quietly, moving his head away from the spoon of soup you were trying to give him. "'M not a baby, I can do it myself."
Joel recovered rather quickly from Abby's attack, after Abby tried to kill him by hitting his head multiple times in the head with a golf club, but before he could die, you and Ellie had the luck to find a gun and shoot at Abby.
Joel could barely talk, move, or stand up after it, but later on, 6 days later, he was almost starting to run again. His stubborn nature not letting himself stay more than 5 minutes laying, you'd find him sweeping the floor of his room, writing, playing guitar, it doesn't matter how much you tell him that it's dangerous—he wouldn't listen and keep doing what he was told not to.
It wasn't a surprise to see him refusing help, he had the habit of putting your and Ellie's safety on top of his own safety, independent if he's the one hurt. He'd kill scientists to keep Ellie safe—and he did it after scientists tried to kill Ellie and use her blood as a cure for the infected.