Disclaimer: I own no part of Sherlock or its characters.
Characters/Pairings: Sherlock Holmes, John Watson, Mycroft Holmes (mentioned).
Genre: Introspective, angst, psychological.
Rating: PG-13/T.
Word Count: 3288.
Warnings: Mentions of past drug use. Drug-related imagery. Mental health issues (specifically: Attention Deficit Disorder and Major Depressive Disorder). Non-graphic mentions of self-harm and/or self-destructive habits/tendencies.
Summary: There are good days and there are bad days. Today is a Very Bad Day. The day after is when everything shatters inside his head, when the engine races out of control, tears itself to pieces. The third day is when John notices.

Day One

There are good days and there are bad days.

Today is a decidedly bad day. In fact, it starts out merely bad (he jolts awake at 7 o'clock in the morning after a particularly restless night, his arm aching and his neck annoyingly stiff), graduates to Bad around midday (all of the experiments in the kitchen are wrong and boring and he wants to just bin every single one but he can't because he knows that tomorrow he will want them, probably, when this passes), and ventures into Very Bad territory about an hour after that (not even the violin is helping because every single piece he plays isn't right, it's too loud or too soft or too adagio or allegro or vivace, it's just wrong, all wrong, all rubbish).

It is around this time that Sherlock realises he's relieved John isn't here. That he's at the surgery, working, curing people, fixing up a fraction of a fraction of all the world's wrongs, making a negligible difference. Oh, there's a part of him that wishes John were in the flat, but it's a small part, an irrational part, and irrational parts are irrelevant to the whole.

No, it's better that he's alone. John would just get in the way. Might even make It worse. Probably hover about, asking questions, treating him like a patient. (He hates being a patient. It's nearly as bad as being a doctor.) Too much to deal with.

Better to be alone.

By half past one, he has made a mess of the living room. Books lie abandoned, face-down on chairs; at least four experiments have migrated from the kitchen; sheaves of paper carpet the floor. He manages to get an absurdly long paper cut on the sole of his foot, and swears so explosively he half-expects Mrs. Hudson to come bustling up and see what the shouting is all about.

She doesn't.

He very nearly wishes she would.

He needs to be moving, needs to be doing something or he'll drive himself insane before he gets another case, and that won't be good. Not good at all. So he cleans the flat.

It takes him four hours. He makes himself do it, even though it borders on being physically painful. (It isn't actually, except for the moments when he nearly convinces himself to give up. Then he deliberately presses the sole of his right foot into the floor and lets the stinging pain dissuade him.)

(And it should only have taken him two and a half hours, but he'd gotten—distracted, stuck, tunnel-blinded while he reorganised the bookcase. And it had been another mark of his failure that he'd only snapped out of it after his mobile went off. Unlisted number, a caller who hung up as soon as he'd answered with, "Sherlock Holmes." Mycroft.)

The accompanying feeling of accomplishment is faint and fleeting and an utterly crap reward for the amount of time spent.

He cradles it to himself for as long as he can.

John comes home late, bearing gifts of curry and chicken masala and basmati rice and three different kinds of naan, and it very nearly makes up for the searing, sickening irritation that squeezes Sherlock's lungs the moment his flatmate starts nattering about the surgery and the patients and Sarah, being stupidly obvious in his attempts to draw Sherlock out of his head and into conversation.

(And it reminds him of why he hates people, why it's better to deal with this alone. John may know, he may accept Sherlock as he is, but he can't understand, not when his brain is wired just like everyone else's.)

He eats his dinner mechanically, silently, just to be doing something.

The box is old and wooden and plain, with a broken lock and hinges that probably need oiling, and it lives inside the nightstand beside the bed he rarely uses.

He hates sleep, hates it for being a total waste of precious thinking/doing/observing/deducing/experimenting time, but right now, at this moment, all he wants is for this to go faster, for this wretched day to be over. Except he knows his body, and he knows that tonight, it will resist sleep no matter how much he wants it, and that is what the box in his lap is for. His legal box. The one with the cigarettes he refuses to smoke, the nicotine patches he needs to buy more of, the sleeping pills that he rarely takes. His safe box.

(It has a twin. This is the ugly twin; the other is beautiful and dangerous and it lives in a dark place that only Sherlock knows but will never go back to. Never. This is his life now, not that. It will never be that again, and, oh, how he misses it sometimes.)

He caresses the cigarettes, counts the patches, downs two of the pills, and waits for sleep to make his eyelids heavy.

Day Two

Sherlock wakes up the next morning with the muscle-deep lethargy that reminds him of why he hates sleeping pills. It's too early to determine what kind of day it will be (brain processes just warming up, percolating, bubbling and snapping), but there is an awful feeling deep in his gut that sends a quiet warning to his head.

He ignores it and rolls out of bed.

Right around the time John comes down for breakfast, Lestrade calls Sherlock with a case, and that ought to make it a fairly okay day, but it doesn't. Sherlock knows it the moment his mobile rings, the chiming like something flipping a switch inside his head, setting everything off.

Oh, he thinks as he answers the call. It's a Worse Day.

It is only through sheer force of will that Sherlock manages, somehow, to keep himself engaged in the conversation for long enough to make the most important connections and relay to the DI the only logical conclusion (The bird, look in the cage, just—look. Yes, I know the bird's been dead for months, but just—look! The—paper, there will be paper, clean paper, sheet music, put down in the cage, take it, it's all you'll need.), but after that everything falls apart.

Everything just shatters. In his head. The glass walls with spiderwebbing cracks, so fragile at the best of times, they just—just come down. The layers of thoughts, of ideas, of fragmented half-memories, they fall out of those neatly-organised, scrupulously-maintained folders in his head, crashing and colliding and superimposing and melting into one another like so much raw data flashing across his screen and it happens in an instant, just an instant that feels like forever.

He curls up on the sofa, pressing his face into the cushions, watching everything that plays against the insides of his eyelids.

(Eleven-year-old Mycroft says don't be daft, you can't be Captain Hook—no, you're not allowed to feed your own hand to an overgrown reptile. Sherlock! but the visual is of a dead man with his eyes plucked out. Enucleation. Some case from weeks ago. He can't find the details, let alone make them stick, not when Mycroft is being a distracting git even in Sherlock's own head.)

(The layers are bleeding into one another.)

(But even Mycroft is not as bad as what happens when layers of the same sense start to flatten together. Melodie in E-flat major, Op. 42, No. 3 is superimposed over when I was younger so much younger than today is superimposed over sitting in a tin can far above the world is superimposed over we do our time like pennies in a jar, and the places where they try to fit together are ragged and cacophonous. It plays in a loop. He hates Tchaikovsky.)

And he hears and watches and tries to find one thing—one thing, just one—to concentrate on, one thing to pick out of the mess and focus everything on, to rebuild the walls around, but it's like grains of sand through a sieve, it all goes right through, slipping away.

John thinks this is another one of his post-case fits of melancholic boredom.

(Depressive episode, something inside Sherlock whispers, vicious and hateful. Major depression. Probability of co-morbidity in subjects diagnosed with—)

He looks at Sherlock, curled on the sofa, and sighs. Says something about getting another case soon, not to worry. Makes tea, sets it on the coffee table. Mutters something about milk or Mike or the market. (Can hear the words, oh, yes, but they are unimportant, so they slide right past.)

Leaves.

Ten minutes later, he sits up, looks at the skull on the mantelpiece, and realises that this is the first Very Bad day he's had since John moved in however many months ago; prior to this, to the past two days, he's only had Moderately Bad days. And maybe it's logical, maybe all of the Bad has accumulated, maybe he has compounded interest, maybe, maybe, maybe.

A not-maybe: It is the worst day Sherlock can remember ever having, but that's not much of a surprise. He has the sneaking suspicion he deleted all of the other "worst days", and now he regrets it, as he'd like to know how he got through them.

Cocaine, probably.

He remembers feeling like this, though. Vaguely. It's undeletable.

Frustration and agitation turned inward.

It feels a lot like self-hatred.

He can't breathe for the want, the need, the memory of white lines and puncture marks that made it so easy to keep his head, his engine, under strict control, on the right track, far away from the thin railing that keeps him from going over the edge. It would be worth it, it would be so much worth the aftermath, just for those fifteen minutes of clarity, just for that, only that, only—

No. No.

This is the price. The exchange. For the cases. For the Work.

(The Deal he made with the Devil-named-Mycroft.)

Without the Work, there is nothing. No John, no 221b Baker Street, no world outside his head. Nothing.

Sherlock puts nicotine patches over the faded marks of habit and shuts his eyes.

Tomorrow. Tomorrow will be better. It cannot be worse.

Day Three

By the third day, he is drowning in a sick ocean of half-formed thoughts, trapped in his own fucking head, and it's hateful because the control is gone, and it makes him want to vomit, to scream, to rip himself apart and put himself together right, and the untended sole of his right foot is swollen and angry from the pressure he puts on it because yes, pain like bright stars across his eyelids and electricity to his brain is the only thing that can keep him on track.

His foot is what finally tips John off.

"Oh, for god's sake, what have you done now?" he mutters when he comes down for breakfast and sees Sherlock hobbling his way across the sitting room. "Sit down."

And by now Sherlock is so tired, so goddamn exhausted with It, with everything, with himself, that he wordlessly obeys. Plops himself into John's armchair and watches as the doctor kneels, picks up his foot, and swears.

"You complete fucking twit." The muscle in his jaw jumps. "Explain. Now."

What is there to explain?

He tries to say, It was the only thing that kept me focussed, but all that comes out, in a cracked voice he hasn't used in nearly a day, is, "It was that or cocaine."

And for a moment, for one awful moment, John looks up at him, so horrified he actually stops breathing.

"Jesus," John whispers. "Jesus Christ. Why? Why the hell wou—" The realisation dawns across his face like a glorious sunrise. Summer-gold skin, dust-blonde hair, pale pink lips, red creeping up his neck. It is beautiful, in its own way. Something Sherlock can at least appreciate, can even focus on, briefly, mercifully. So of course, of course John ruins it by saying, "It's the AD—"

Sherlock cuts him off swiftly, clapping his hand over his flatmate's mouth and hissing, "Don't. Say. It." (Inside his head: A is for action, a is for addict, dee is for desperate, dee is for depressed despised dysfunctional deductive defective detective deficit disorder denial and it's overlaid with snapshots of secondary school. Shut up, shut up, shut up, he tells himself. Like a constant litany, always in his brain.)

John's eyes narrow, but he nods, looking pointedly at Sherlock until he removes his hand. His lips are thin, pressed together like pages in a book.

"It's that, though, isn't it? The—" As John looks inward for a moment, Sherlock observes, reading his thoughts in the lines of his face, in the tightening of skin around his eyes. He's searching for a word, any word, something that Sherlock's said, something that he's called it, something that won't make either of them flinch. After a moment, John takes a breath, carefully watching Sherlock, anticipating his reaction. "The... deficit."

The deficit. Non-specific. Acceptable. For now, at least.

(He remembers saying, "I don't hate it, you know. The—deficit," but can't for the life of him recall what he'd been thinking at the time; he does hate it. Hates it with every fibre of his being.)

"Yes," he says aloud, nodding jerkily, his eyes not quite on John's face, but on some point just over his head. "That."

It comes out a snarl, bitter and awful and hurtful, and the silence that follows sounds sharp as the shattered glass inside Sherlock's head. It makes every single thought (des reflets d'argent, that go sailing in the background, the foreground a stream of this, it's always this, don't look at him don't read his body language just don't you know you won't like what you'll read there) seem even louder, even more unbearable, even more overwhelming. No way to shut it out. Useless to try. Just deal with it, endure it.

He doesn't even realise that he's tensed up until his flatmate (flatmate doctor blogger assistant soldier colleague friend friend only friend I will never tell him so why is he still here how can he stand this me all of it?) gently pats his ankle.

"Bandages," John pronounces after a moment, rising slowly. "Don't move. I mean it. I'll be back."

Where would I even go? he doesn't ask in reply.

And suddenly, Sherlock feels the urge to laugh press hard against his chest, constricting his lungs. He considers repressing it for all of a half-second; he's teetering right at the very edge of hysteria, and he knows that laughing, giggling, will push him over that edge. But his impulse control, tenuous on the best of days, has all but snapped, shot straight to hell (like John's shoulder—no, fuck off, shut up), and really, it's either this or crying, and he's not a crying sort of man. So he thinks, Why not?

And lets go.

When John returns, he doesn't ask why Sherlock's laughing or what he finds so unbearably funny. Perhaps he already knows; Sherlock can never be too sure what his flatmate does or doesn't pick up, but emotions—yes, emotions are usually John's area. Maybe he knows. Maybe he can hear the hysteria and the loathing and the exhaustion.

Maybe he can't.

Either way, all he does is settle back down on the floor, pull Sherlock's foot into his lap, and tend to the wound.

It is a long while later (maybe; it could only be a few minutes, but time... time is so funny when he's like this) before Sherlock finally stops laughing, slumps into the back of his chair, and tells John the truth.

"Everything is shit," he says, and it sounds almost like a sob, but not really. "Everything. Do you even understand that? Do you get it?"

John is silent for a moment, a thoughtful moment, and when he replies, "No," it is honest.

(The bandages are nice and clean and tidy around Sherlock's foot. Finished. And yet he hasn't moved. Why hasn't he? What is he waiting for? Me?)

"No," he continues slowly, "I don't get it. No, don't make that face, please—just listen to me, Sherlock. All right? I can't see into your head or feel what you feel at any given moment. I don't understand. I can't. You have to tell me. Do you—No, you're making that face again." John lets out a frustrated breath and sits back, drawing his knees up, raking his hands through his hair.

(What face? I can't see myself in the mirror of you, not when you've gone opaque like this. Which face do you mean? But he sort of knows which one, can feel it in the clenching of his jaw, in the crumpling of the skin of his brow, in the tightening of the right corner of his mouth. He hates that face.)

(He hates the one John is making even more. Helpless and frustrated and hurt not on his own part but on Sherlock's, like he thinks something is unfair but doesn't know how to voice his disapproval of injustice.)

"What is it like inside your head?"

Sherlock jolts upright, his spine cracking a little, his eyes sharpening.

John is looking at him straight-on, something grim in his gaze, something like memory. His voice is low. "That's what I asked you. Remember?"

"Of cou—"

"I'm asking you again. Right now, at this moment, what is it like inside your head? Tell me honestly. Make me understand, Sherlock, because I'm just an idiot. I'm not you."

And Sherlock has to suck in a breath because the way the fingertips of John's right hand rub against the knuckles of his left say nervous sincerity, and the way his tongue wets his lower lip speaks of genuine interest, and the set of his shoulders tells of concern and patience and something Sherlock doesn't have enough data to define. It's... overwhelming.

How could I deserve this? he wonders as he tilts his chin up, rests his head back, shuts his eyes and basks in the odd warmth in the space between them.

But he doesn't say that; what he says instead is, "It's like drowning in a sea of glass, where every shard is like a thought, and each cut it makes bleeds more glass, and it's impossible to avoid. And..."

And After

He doesn't expect it to be all right again, just because he sits across from John for an hour and a half and puts his head into words. He doesn't expect the walls and layers to instantly mend, or for the cravings to go away, or for everything to become less irritating or hateful or shit.

And they don't. His walls are still shattered. The cravings remain. The next morning he wakes up and he still wants to crawl out of his skin, to cut open his head and physically remove parts of his brain. Nothing is different because there is no magic cure.

But every day John asks, "What is it like inside your head?" and every day Sherlock answers even when the words stick in his throat like a molasses scream. Sometimes the telling makes him feel heavier, angry, drowned; sometimes it makes him feel lighter, empty, sated. Sometimes he can reply immediately; other times he can't find the right words until John is already in bed.

There are ups and downs, and times when even John's patience runs out. But little by little, things will mend. One day, Sherlock will wake up, look inwards, and see the glass walls back in place, fragile with cracks and chips, but standing.

And Sherlock, being Sherlock, will not smile at the sight—but it'll be a close thing.

Notes:
Lyrics credit to: The Beatles, Bowie, The Bravery, ima robot, Charles Trenet, and Jack Lawrence. Bonus points if you spot all the lyrics. Super-extra bonus points if you get the Tinker, Tailor, Soldier, Spy reference.

Aaand Lestrade's case is—embarrassingly enough—based on something I remembered from a Clue, Jr. book I read as a kid.

Thanks for reading!