"I bought milk," John calls from down the stairs, and Sherlock can hear his footsteps up to the landing and through the door but, as usual, he ignores his roommate and burrows further into the depths of the sofa. The only difference is that today, his head pounds and his hands are clammy but the room is too cold, then too hot, and he just wants to get rid of all this fabric swathed around him, trapping him in burning heat, so he pulls off his robe and shivers. It's cold. He can't think. The machine that is his brain refuses to work for once, won't tell him what's wrong, and oh god it's freezing and his teeth chatter and he gropes blindly behind him for his robe.

A warm hand descends on his forehead and he vaguely feels himself being rolled over, stares dully into a swimming pair of brown eyes that narrow, flicker down the length of his torso, suddenly disappear. The light from the ceiling is too too bright and Sherlock wishes he could make it stop, where is that gun? It's so cold.

"John?" he mumbles. He raises his arms to block out the light, and for a moment is plunged into delightful darkness. The distant sound of someone's voice manages to interrupt his moment of peace, then he's being hoisted upward and a pill is pushed through his lips and cool water slides down his throat. He slumps back down.

"...got the flu..."

It's so cold and Sherlock is so tired. He wills his brain to work, mind over matter, but it's rebelling and he feels lethargy pooling in his arms and legs and neck. He clutches at the blanket that has come to rest over his chest, curls himself into a ball. Something cool and damp assuages his throbbing temples, but it makes him feel even colder so he swats feebly at the cloth and hears it land with a splat on the floor. It is returned immediately to his forehead.

"John," he repeats. He concentrates on getting the right words out. "Brains... freezer. Was the... cat, Mycroft. Lestrade..."

"It's alright, Sherlock," John says, and Sherlock sinks as far as he can into the pillows of the sofa, letting out a sigh. His eyelids are heavy, and it's almost too much effort to try and hold them up. He feels sticky, slick with sweat, goosebumpy, startlingly chilly, but from his side he feels John radiating warm heat, hears him drag over the footstool and flip open his laptop. With the sound of the keyboard, Sherlock drifts into sleep.

...

Sherlock snaps in and out of dozing, tossing and turning and kicking off his blanket or throwing the cooling cloths across the room. When he finally wakes up he leans over the side of the couch and retches four times before coughing up the contents of his stomach. John's fingers encouragingly stroke the back of his neck as he coughs and coughs and coughs. When his eyes close again, his tongue is sour with bile but John's fingers are still comfortingly tangled in his hair.

...

"I'm not sick any more," Sherlock says stubbornly to the ceiling. "There is no reason to keep me here." The room, after all, has stopped spinning as much as before.

John doesn't reply, only raises his eyebrows as he continues to type. Sherlock coughs wetly, draws a rattling breath, and crosses his arms. "Look, I'm perfectly fine. I hope that's not about me. John, you'd better not be writing about me."

"And so, I deduced that Sherlock Holmes is a great bollocksing annoyance and needs to remember that I am a medical doctor and can in fact tell him exactly what he can and cannot do while sick with the flu," John reads pointedly.

Sherlock pouts childishly, and curls back into a ball.

...

He is peering through his microscope at a sliver of liver obtained under dubious circumstances when John comes through the door, dumps the groceries down on the counter next to Sherlock's stacks of Petri dishes, and drags him back to the couch.

...

A week and three days passes and Sherlock is hunched over a dead clown as sirens flash red and blue in the background. John stands by his side as the people around them take bright snapshots of scenery and cluster in groups presumably to mutter the same old things about the man who appears to be staring blankly at the clown's left elbow. John is fairly sure it's worth standing here in the freezing cold just to watch Sherlock's brow furrow as the gears turn at impossible speeds inside that mysterious and wonderful brain of his.

All of a sudden Sherlock straightens in that ridiculously graceful way and John thinks he must have discovered something incredible from the fold of an ear or the dust under a collar but instead he grasps John by the shoulders, stares at him for a long moment, and smiles. "Thank you," Sherlock says sincerely.

And then he spins away, leaps into the air with a feverish whoop and a cry, insults several of Scotland Yard's best and solves a mystery.