A/N: Originally posted to my AO3 account. Thanks to my lovely beta Shanzay and to Charlotte for leading me to Shanzay and encouraging me to continue with this story.
Definitions of non-English words are in the endnotes.
Please note that this story contains references to hallucinations and mental health issues, which may be triggering to some people.

"Genius is a curse. That's how I look at it. Some think that the brilliant comprehend the universe in a way the rest of us can't. They see the world how it truly is—and that reality is so horrible the lose their minds. Clarity leads to insanity."

- Harlan Coben, Caught

Sherlock's mind was his pride and joy. He relished in its sharpness, the way words would pop into his mind like polished daggers, ready to cut his opponents and make them bleed. He took pride in its eye for detail, how pieces of evidence would start to form connections and blossom into an elegant web – obvious only to him, whispering its secrets and its stories in his ear. He loved how everything was so vivid, how colours, scents and textures could mix and meld and yet remain firmly distinct, each jostling to be the subject of his attention. The drama, the flair of life, evident only to his keen mind (how in the world did people live without archenemies?) put a bounce in his stride and a manic glint in his eye. When focused, his mind was the most dangerous tool in the world. When focused, his mind was a finely-tuned instrument without rival. When focused, Sherlock's mind was the best part of himself.

Sherlock's mind was his worst enemy. The shattered trains of thought (because only an idiot would follow a single train of thought at a time) swerved and collided, sparking and scraping against the inside of his skull. The smallest detail blazed like a supernova, and even when he closed his eyes, they continued to burn through his eyelids in rapid succession. They screamed to be heard (followed by the whispers, always the whispers), to be seen, to be observed, deduced and given a purpose.

He had been an insomniac for as long as he could remember. It wasn't that he couldn't sleep; rather, he forced himself to stay awake for as long as physically possible. It wasn't the sleep itself that shook him, for he had never been plagued by either nightmares or dreams. But it was the in-between times that left him raw and bare and struggling for purchase: those hazy moments between sleep and wakefulness, when his filters were down and the threads of thousands of cases, real and imagined, twisted and tangled into a writhing knot that snaked low in his gut.

The pink (numbers, always numbers) it's the phone (with the pips and the semtex) which was stolen (acrobats with swords and paint) swimming in a pool (but the railroad, we can't forget the railroad) and John was kidnapped (and John was abducted) and John was in danger (and John killed the danger) but John was in danger of not being in danger (of losing John) and I helped that, didn't I? But Carl Powers was a skeleton going around the garden (burning in the sun) because hearts are burning and lives are at stake and that matters but it doesn't because I can't save them.

He couldn't save them.

Lives fell through his fingers like sand, like the dry dusty sand that trickled through an hourglass, marking the time (always the time). And time was his enemy, because he had too much of it, because he was Sherlock Holmes and no one could keep up with his massive intellect. And so he waited for them to catch up. He waited and waited and slowly suffocated, smothered in toska, entrenched in litost,while others sneered and brushed it off as mere boredom.

Boredom. That's what they called it. It was an idiotic word for idiotic minds. They could not, would not comprehend the true nature of his mind. They'd go insane. Then again, wasn't he? Boredom did not describe the way spots would eat away at his vision until it was safer to stay on the couch than to try and walk anywhere. Boredom did not describe the way his throat would constrict until every breath sent a shudder through his entire body and he wondered if someone could drown in air (a preposterous and completely unscientific thought). Boredom did not describe the way shapes would appear at the edge of his vision, increasing in detail and size until they became full-fledged figures, grinning caricatures of his latest case, smirking memories and sneering fictions, faces to the omnipresent and sometimes, he believed, omnipotent whispers:

Why was I killed Sherlock? What did Moriarty want with me? Why weren't you fast enough, strong enough, smart enough? Who are you but a lost boy, making up a fancy title to hide the fact that you will be alone forever?

He would pull out the gun, intent to shoot them all straight between their imaginary eyes, but halted each time. Instead, he shot around them, tracing petty figures and faces into the wall in the hopes that the other figures (with faces, with voices, with backgrounds he refused to deduce, because that made them real) would flinch and disappear. But the only thing that was flinching was John and this was wrong, the voices said, this is not how you live with someone with PTSD, but Sherlock wasn't supposed to listen to the voices and John didn't know that his flatmate was insane and if John knew, John would leave. John would leave Sherlock alone with all the voices.

And so the man (the boy) with the sharp mind that could shred his opponents' arguments into shreds (don't run with scissors, don't run with knives, because you can cut yourself, because the blade runs both ways) slowly drowned, lungs filled with voices, secrets and bitter, lonely guilt.

Notes:

Toska: Russian word with no simple English translation. Vladmir Nabokov, a Russian writer, once said: "No single word in English renders all the shades of toska. At its deepest and most painful, it is a sensation of great spiritual anguish, often without any specific cause. At less morbid levels it is a dull ache of the soul, a longing with nothing to long for, a sick pining, a vague restlessness, mental throes, yearning. In particular cases it may be the desire for somebody of something specific, nostalgia, love-sickness. At the lowest level it grades into ennui, boredom."

Litost: Czech word also with no simple English translation. The closest definition is a state of agony and torment created by the sudden sight of one's own misery