Frisk doesn't need to worry about getting up. S-4 knows exhaustion when he sees it, and he knows how to carry someone who's having trouble moving. In an instant, they're up in S-4's arms, and he starts walking down the hall, smiling softly. He's tired too, and he might be barely awake when he gets them to the bedroom, but he doesn't much care if it means Frisk and everyone else is safe.