The day Sherlock passes out in front of him, John's blood pounds through his veins in a way it hasn't since Sherlock was shot. Still, he's never been one for panicking as a military doctor, and so he's all precision and profession. He gets Sherlock to the hospital in record time and worries that perhaps something's happened with the old wound, or that the drugs finally took their toll, or that Sherlock might have been slipped something by an enemy.
So it's a relief, of course, when they run the tests to find that Sherlock's merely flu-ridden, dehydrated, and fevered. Bloody idiot was too obsessed with solving the case to eat properly, of course it's going to hit him harder if he's sick, John thinks with annoyance, then chastises himself for not seeing the signs.
When Sherlock comes to a little later, he's halfway out of bed, eyes wild with fever and excitement. "No, John, I'm fine, I've solved it. I just need to check if his landlord has a-"
John interrupts with a firm hand to Sherlock's chest, pressing him back against the mattress. He's having none of this at all. His eyes are hard and unrelenting, and his tone is so firm and clipped that even Sherlock Holmes dare not argue with the solitary command John utters: "Bed."