When John comes to, it takes him all of 5 seconds to sense his surroundings before he figures out exactly where he is. Everything he takes in is instantly recognizable; the stark bright lights that penetrate his eyelids so much that he has to shift his head sideways, the soft, constant beeping of the ECG beside him in the midst of distant ringing of reception phones and the wheeling of carts past the corridors, the fresh smell of linen he's wrapped in and it's somewhat papery feel on his skin.

It takes him a bit longer to remember exactly how he'd ended up here. Yet again.

After a minute, he remembers. He thinks that if he had the strength to open his eyes right now, he'd be rolling them.

When John Watson underwent the transition from unknown retired army veteran with mysterious psychosomatic limp to famous blogger, flatmate and colleague of the world's only consulting detective, he knew he'd be seeing more of St Barts Hospital. He knew this hospital held two main attractions for Sherlock: one, therein lay precious chemicals or scientific equipment that was either too expensive for Sherlock to purchase himself or too large or hazardous for 221B to contain, and two, dead bodies. The wealth of mystery and subjects of experimentation lying within these walls were enough to keep Sherlock away from his flat for days on end, when cases were sparse and Sherlock was driven up the wall by boredom.

So it came as a surprise to John that his familiarization with Barts came through another means entirely.

Documenting Sherlock's cases to the public domain led to a quick rise in his clientele, and while not all of them required Sherlock to so much as lift a finger, the mere abundance of cases meant that there were more that did require Sherlock (and by extension, John) to leave their flat more often. As a result, the number of encounters they've had with people who weren't so happy with Sherlock meddling in their business and foiling their crimes grew, and John found them both in the habit of getting injured more and more put it simply, he found the instances of him being wheeled into Barts more frequent than him walking into Barts on his own accord.

Oh, the irony. He'd trained as a medical student here, and he'd worked here for a few years after he'd gotten his license to practice, but those days were eventful, and time went by very, very quickly. He never thought he'd get tired of seeing the place as a patient. God, it was much more boring on this end of the stick.

John opens his eyes and tries to get up, and all at once a flash of pain blazes through his skull. He winces and touches his forehead. It's covered in about two inches of dressing.

"Great," he mutters, lying back down slowly, "Just great. What have I gotten into now?"

His eyes are open now though. He rolls them gratuitously. It hurts his head even more. Dammit.

"John!" someone calls, and John turns to see a elderly nurse with thumb-sized eyebags and a golden nametag with the sparkling words HEAD SISTER across it walking in. "You're awake. Good. I need you to help me sign off these prescriptions, it's past midnight and the bloody foundation students on call tonight are late as usual."

John lets out an exaggerated groan. "Come on, Stella, not again? Can't you see I'm bedded? And besides, I thought those hooligans only did A&E on Tuesdays and Thursdays? It's Friday today."

Stella laughs, handing him a plastic cup of water before picking up the inpatient file at the end of his bed. "Saturday, love. You were under all day yesterday. Anyway, I'm just kidding. Dr. Smith told me to check your vitals as soon as you were awake and I figured that was the quickest way to find out."

"Ah. No hello, or nice to see you again, or how are you feeling. Just ask for a favor. Nice way to greet a patient."

"A returning patient," Stella corrects him, scribbling into his records. "Who's been admitted here more times than homeless junkies in all of Holborn have."

"Are you calling me a homeless junkie? Ouch."

Stella grins, checking his ECG charts and ticking off a few more boxes in his records, "You responded to your name, you remember what day you were admitted, and you have the same bland sense of humor as ever. Or lack thereof," she says, eliciting a hurt look from John, "I'd say that blow to the head didn't cause too much trouble."

"Still hurts a bit," John says, rubbing the wound on his head for effect. "We were up against three men. Armed robbery. Took them out before they could steal anything, but I took a bludgeon to the head in the process. I feel fine otherwise."

"Lucky for you. The cut was pretty deep."

Someone knocks at the door. "Stella?"

John sees a chirpy face peep in, underneath a head of blond pigtails. Upon seeing John, her face lights up like a Christmas tree.

"Alright there, Lucy?" John says.

Lucy is a nurse from the paediatric ward. She's also Stella's niece. She helps out in A&E when her ward is quiet. John likes her. She nicks lollipops from the paeds reception for him whenever he complains about his pain. He thinks she has a crush on him because sometimes she'll adjust the temperature and turn the telly down when she thinks he's asleep. John thinks she's the only person in the world who's happy at how often John gets injured, because then she'll get to see him more often.

"Good, John, thanks." Lucy answers. "Nice to see you're awake. Would you, er, like something to eat?"

"Just the usual, thanks," John says, "And can I have the chocolate pudding for dessert this time? I keep getting the apple pie. The crust is all stale and cold."

"Coming up," Lucy says without a moment's hesitation. "Stella, I've got a problem in ward 11. Lady says she can't feel her legs. Even though she's standing upright."

Stella sighs and hands John his file and a pen. "Do you think you could do your temperature and pulse yourself?"

"What, now I have to do the nursing work too?" John wails. "What next, will I need to diagnose myself and sign my own prescriptions? It's illegal, you know."

"Oh don't be a baby. We already have a bigger baby next door. God knows how long he'll be staying here this time."

"Sherlock? He got hurt too?" John sits up immediately. He doesn't know which unsettles him more, the fact that he knew 'baby' was a reference to Sherlock, or the fact that Sherlock was hurt. "What happened to him?"

"He'll be fine. Don't worry, your tally's still higher than his."

"No, wait Stella, I mean it, what's wrong with-" John calls out, but Stella's already walked out of the room.

John huffs.

It started about a year ago, when he and Sherlock realized their presence in the A&E wing of Barts was becoming something of a fortnightly routine. They had just concluded a case regarding a blackguard, a particularly gruelling case that involved him and Sherlock breaking into a house in the middle of the night (which was a terrible idea, and one that John only carried through because he couldn't stand the idea of Sherlock endangering his life on his own). In the end, the deed was done for them by the hand of the blackmail victim herself, and they might have gone off safely if the walls surrounding the house weren't so bloody high. Sherlock in all his agility flew over the wall effortlessly, but John had some difficulty jumping up and over it (it wasn't his fault he was of average height.) He finally did jump across, only to land on his bad leg, and the audible crunch was enough to tell him that the break-in was, indeed, a bad idea. His resulting two-week stay at Barts was torturous, and it only soothed him to see that it took as much a toll on Sherlock, who only admitted himself with a scrape on the elbow. John didn't mean to be so miserable then, but he couldn't complain when Sherlock, in an attempt to cheer him up, suggested they keep a tally on their injuries. 20 points were scored for a gunshot, 10 for a broken bone, 5 for a torn muscle ligament, 10 for burns second degree or higher, and 3 for cuts, scrapes and mild burns. In his self-pity, John insisted on a 50-point handicap for his readily and permanently-wounded shoulder, and Sherlock graciously conceded it. That cheered John up instantly.

Since the Case of Charlie Milverton (which John imaginatively named after the blackguard himself, much to Sherlock's understandable dismay), times at the Barts A&E were much more bearable. Their points mostly came in threes, and twice Sherlock cheated by going after the criminal alone-cases in point being The Naval Treatment (a cut to the hand) and The Lone Biker (a broken finger). That was a year ago. Sherlock's tally is now 50, to John's 73-no, 76, if the way his head feels right now is any indication. Could be worse. Better check the medical reports to be sure.

John opens the purple file in front of him. He stares at the page of blood counts and frowns. Turning the page reveals a chest X-ray film. Lifting it up towards the light, he examines it for half a second before his mouth drops open, horrified.

"STELLA!" he cries out, at exactly the same time he hears her name being called just as loudly from next door. By Sherlock.

Stella appears a minute later. "What's wrong?"

"These bloods, when were they taken?"

Stella looks at the chart. "Yesterday, why?"

"His creatinine and neutrophil levels are outrageous. And..." John moves his finger down to blood sugar levels "..have you been giving him glucose?"

"Him?" Stella looks at him questioningly. "What are you talking about? This is your file."

"No, it's Sherlock's."

"How do you-"

A knock at the door interrupts them both. It's Lucy again.

"Stella, Sherlock's being... difficult," Lucy says, clearly distressed. "Keeps insisting he's got John's file."

Stella looks from John to Lucy, confused.

"Oh bugger this, I want to see him." John says, pulling the electrodes off his body and standing up.

"John you're not supposed to be up!" Stella moves to resist him. He gently pushes her away. The pain of his throbbing head injury blinds him momentarily, but he ignores it.

"I'm fine, I promise." John assures her, standing straight. "See?"

Lucy helps him walk anyway.

They step out to the corridor and enter Sherlock's room next door. There he is, lying on a bed in the middle of the room. Sherlock is not in his normal clothes, like John is. He's wearing the standard Barts patient gown, and John's heart drops to see what he'd expected-a noticeable bandage around his chest, protruding from underneath his gown.

"Sherlock," John says.

"John!" Sherlock looks at him, baffled. "You're... alright."

"I told you he was," Lucy says.

"Well, you wouldn't have known that from the appaling figures in his bloods or his CT now, would you?" Sherlock demands, thrusting his patient file at her.

"Wait," John interrupts, "That's what I came in here for. Sherlock, are you okay? They fixed your rib then? I saw a T4 fracture on your X-ray, it looked pretty bad."

"My X-ray? No, I'm fine," Sherlock says, blocking John from examining him closer, but John catches him wincing as he leans on his left side. "I told them your CT showed significant signs of a contusion, but they told me it was none of my concern." he continues, glaring at Lucy. Sherlock doesn't get along well with Lucy. Or Stella. Come to think of it, Sherlock doesn't get along well with any of the hospital staff.

The nurses look back and forth between Sherlock and John.

"What's going on?" Lucy asks, clearly confused.

"The files!" John and Sherlock exclaim at the same time.

Stella grabs both their files and examines them. "But your file names are correct. How do you know your bloods and scans belonged to the other and not anyone else?"

Sherlock and John look at each other awkwardly.

Oh God, I know what his regular blood levels are. I can tell Sherlock from his chest X ray. What does that say about me?

From the way Sherlock's avoiding his gaze, John knows he's thinking the same thing too.

Sherlock clears his throat unnecessarily. "Oh please, it's all there," he scoffs. "Hardly a glitch, is it? Sure, we're both bloodtype O-, but if that was cause enough for a switch then your hospital is in serious risk of killing an eighth of its patients right now."

John swallows, and points to Sherlock's chest X-ray. "Apart from the glaring fact that the broken rib X-ray is in my file when my chest is perfectly fine, you can tell just by looking. His, uh, clavicles and sternum are more pronounced. His rib cage has a... typical distribution. It's obviously Sherlock's. And besides, his bloods should tell you everything. No one else has such consistent haemoglobin counts in every blood test."

Sherlock stares at John, his face positively glowing at this information. John's afraid of coming off as seemingly pathetic that he knows this, but Sherlock counters it with an equally flattering observation.

He holds up John's CT and simply says, "I... recognized his sodium/potassium ratios. And the cranial measurements in these scans match those of John's exactly. Fairly straightforward."

John gapes at him, his face reddening. "You know my cranial measurements?"

"Of-of course I do." Sherlock says.

John's heart skips a beat. Here is a man who's trashed all knowledge of the solar system, who says all knowledge outside of his cases is transport, useless waste for his brain, but who also considers John's metabolic ratios relevant enough to keep in his memory. That means something to John.

Sherlock clears his throat again, straightening his face. "Which is why I suspected John was very likely to have gotten brain damage, and why I specifically insisted upon seeing him myself-"

"I'm fine, Sherlock, really," John says, touching his head, "Just a little cut."

"You're both right," Lucy says, checking the patient ID on their charts. "We've mixed you up apparently. Sorry about that, John." she looks directly at him. He notes she doesn't apologize to Sherlock. "I guess when paramedics admitted you together they didn't think to separate your records. They're right beside each other at the patient catalogue, after all. What with you two coming in as a pair every time and all."

John shrugs. "Well, now that that's sorted. Stella, Sherlock needs glucose. I can't believe he's stayed awake this long without it. And Lucy, I'm still waiting for my supper."

Stella and Lucy nod, and head out to do as they're told. John glances to Sherlock. "Mind if I stay here and watch the telly with you?"

"Not at all."

"Are you sure you're alright?"

"Yes, John, don't worry about it. I suspect it's a minor fracture."

"Good."

"But it's still a ten on my score."

"No, a fracture doesn't count as-"

"Yes, it does."

"Fine. I get a five for my head, it feels deep."

"Don't be ridiculous, you're talking perfectly normally. Three should do it."

"Four."

"Three. No bargaining."

"Fine."