Disclaimer: I am not a medical professional. All research in this work is gleaned from studying the NHS website et al, and I cannot claim that I will get everything right 100% of the time. If you notice any errors, please feel free to shoot me a PM, and I'll make the necessary corrections.
I have never been a planner, so I have absolutely no idea where this story is going. Makes the "Mystery" tag rather literal, I suppose.
Inspired by Nolan's "Inception"/ BBC's "Life On Mars".
My pal I-AM-SiriusLOCKED wrote the summary, since I clearly cannot do brevity. If you've ever googled 'Avengers fanfic' you will have come across her. We agree to disagree on Stucky.
'Would you just stop doing that?'
Sweat dripped down Sherlock's upper lip.
His skull had been placed in a metal baler.
The machine was toying with him- torturing him.
It could have been over in seconds, but instead there was a set of blades- a row of teeth- a "Odaxelagnia's Anonymous Meeting" of fangs- gently tapping their way over his cranium, like a fly using his scalp as an artist uses their rag, like a blind man navigating his way across the no man's land of his subconscious, like a prospector probing into his soul to see if it was still intact.
John sighed, and an incisor pressed against Sherlock's parietal bone.
He winced.
Sherlock opened his eyes.
Through the cover of his blanket, he saw John lower the newspaper, and he winced again at the rustling of the pages, and the way his eyes burned.
Better to keep them closed.
Even with the curtains drawn, and his vision partially obstructed, it was as if Heaven had picked a really opportune moment to reveal its existence.
And even with Mrs. Hudson away for the weekend, every breath was an air-raid siren, an earthquake, a distraction.
John's reply was muffled by the ringing in Sherlock's ears.
It was like that idiot off "Britain's Got Talent" was performing their highly-original "glass harp act" right inside his ear drum. The effect was a magnified version of what it had been the night he'd seen it on the telly: irritation, followed by the urge to maim.
'What did you say?'
'...I said, "stop doing what"?'
Sherlock winced again. 'You don't need to shout, John.'
'How was I- you were the one- oh, forget it.'
Sleep alluded him, and the irony wasn't lost, after years of trying to allude sleep.
This was going to be a long 24 hours.
Particularly if John insisted on reading the paper in such an obnoxious way. Couldn't he just use the app?
'Sherlock?' John said a few minutes later.
The newspaper was put down again, and it sounded to Sherlock like an entire forest being felled.
He managed not to wince, but only because wincing was getting boring.
'Hmmm?'
Sherlock wondered if he could have more sumatriptan. He'd enjoyed the injection, though John had made them administer it via his right thigh, in case having a needle piercing his upper arm brought back too many good memories.
Every heartbeat caused a rush of dizziness and nausea, but nonetheless Sherlock moved into his "Thinking Position". John would be difficult to convince, especially with his having an addictive personality, but another syringe or two would hardly give him sulfhemoglobinemia-
'What am I supposed to stop doing?'
'I'd just like you to stop being so loud, John. I know you can't help it, but… I have a headache,' Sherlock wined, unable to stop his mouth forming a pout.
John sighed again, and Sherlock told himself he wasn't sighing so loud on purpose. John did like to be dramatic.
'Stop pouting.'
How could he tell?
Anyway, it only made him pout more.
Sherlock knew without checking that John was now pinching the bridge of his nose.
'Just hold your breath and don't move. For a few seconds. Please.'
There was a sort of choked noise as John restrained himself from heaving another sigh, and then there was quiet.
It wasn't perfect: there was still the scream of the birds outside, the roar of the cabs below, the deafening sound of his own breathing (which also had the consequence of making the left side of his skull throb to the rhythm).
But Sherlock's shoulders still slumped, he still let out a breath he didn't realise he'd been holding, relaxed muscles he didn't know had been tensed. Maneuvering himself until he was horizontal on the sofa, he began to seriously entertain the idea of sleep. He'd stopped dreaming since the accident, but that was okay, if a little boring.
45 seconds later, John spluttered an exhalation.
'Excellent,' Sherlock commended. 'Now, if you could just keep doing that-'
'Sherlock?'
John was using that low and dangerous voice that meant he had done something wrong, and Sherlock knew his head was tilted to the side, his eyes fixed on something on the opposite wall, his jaw tensed. He had to tread carefully.
'Yes?'
'Did you really just ask me if I could hold my breath for the rest of the sodding day?'
'Well, you can take breaks, naturally, but I-'
'No.'
Sherlock opened his eyes, and struggled into a sitting position.
'John-'
'I should have ignored your protests and bought those bloody noise-cancelling headphones on the cab ride back from the hospital,' John grumbled.
'I can't have my senses completely impaired, John. It's dangerous.'
'Please stop grinding your teeth,' Sherlock whispered a short time later.
John sighed, but Sherlock knew better than to say anything.
'You look like a right prat with that blanket over your head, do you know that?'
They both chuckled, even though laughing made everything ache worse.
Tension somewhat alleviated, John continued: 'I know you've had a really- a fucking awful time this past month, Sherlock, and I'm so happy you're home again, and that the attack doesn't seem to have done any serious, lasting damage...'
Sherlock waited for the 'but'.
'But… we just need you to make it through the rest of the day without dying, and then I can be back looking after Mary, and you won't be driven crazy by my daring to function like an ordinary human being…'
He began to zone out.
'...keep your complaints to yourself?'
Sherlock promised that he would.
10 minutes later, John's phone began buzzing [Mary], and there is the clink of nails against ceramic as an auto-piloted, reaching hand continues on its path...
The mug smashes on the floor, and there is swearing.
The commotion has Sherlock clawing at the sofa like some poor 15th-century bugger who'd been accidentally buried alive. His blanket falls off- which is good because he is too hot, but bad because he is too cold.
John swipes up his phone, sweating, but it stops ringing before he gets it to his ear. He curses.
'She's not in labour,' Sherlock gasps, shuddering at the shock of it all, the sudden change in light and temperature, the fact that he's not seeing one John, but two-
His thumb is on the "call back" button, but John stands, immobile, choosing instead to observe his flatmate's suffering.
'Sod this,' he says. 'Sod this. You're like Mrs-Sodding-Bennet.'
Once Sherlock recovers from the heart attack John induces by slamming the door, the silence is wonderful.
He keeps the time by the pulsing of his head, and John returns 780 beats later, in a slightly better mood, judging by the lightness in his step. Mary no doubt had soppy news about the baby. Sherlock thinks of how much noise it will make when it's born, and whimpers.
John moves across to stand right in front of him, and he concludes that that grin is bad news.
'You're getting another injection, some lunch, and then we're going to the neurologist.'
Sherlock stares as John pulls his phone back out of his pocket.
'...John?'
'Hello, yes, I was wondering if I could make an urgent appointment for an hour's time?
'John! No, you can't do this- John! John please…'