When there is too long without something to focus his mind on, his mind focuses inwards and begins to rip itself apart.
When there is too long without the feeling of danger, his mind compensates for the lack and begins to create its own.
John wakes with a horrible start, chest heaving and hands shaking, and he rips the sheets off, certain he will see his leg covered in blood.
It's not. It's not. And even when it had been, it hadn't been his blood, for all his mind kept insisting in nightmares and psychosomatic limps that it had.
He sits up and digs his hands into his short hair, trying desperately to slow his breathing, for his brain to realize fully that he is in a nice, safe - relatively - flat in London, not in Afghanistan with snipers trying to pick off the medics.
From downstairs, he can hear Sherlock's violin, which he thinks is what actually woke him in the first place. He's playing rather aggressively, alternating between mezzoforte and forte and fortissimo, as though the time on the clock and the idea other people may be sleeping means nothing to him, which it probably doesn't. It's something very modern and repetitive with a touch of classic throwbacks that remind him a bit of Vivaldi. But mostly, at first, it feels like the same run of notes over and over again. But--it's not. There are little, subtle differences, little changes in the lines and contours, little shifts in all the sameness. It's very unlike Sherlock, yet like him - John can only imagine the concentration it must take to play something that seems like it's all the bloody same until you actually open your ears and listen to it.
He remembers the first time he heard Sherlock play something like this; he thought he'd go mad, same thing drilling into his head over and over and over again when his brain was already frayed and on repeat, and then, all of a sudden, oh, hey now, that part's different, and then whole thing had shifted into something that was the same but somehow new, full of a rich subtlety of movement, and in that moment, it became captivating. John can only imagine the concentration it must take to play because it takes all John's concentration just to hear the tiny shifts; the moments where one note is different, or is held out shorter or longer, where the pattern breaks and swirls off into a new one that is almost the same but not, and it's a distraction his mind leaps for, to get away from twisted up nightmares from memories of blood and bullets.
He always thinks he should ask Sherlock what it is he's playing, but he never does - Sherlock only seems to play those hauntingly repetitive violin pieces late at night, and John only wakes for them the nights his hands are fisted in his sheets and his head is full of explosions and blood. Sherlock never plays them in the daylight, when John could ask him what it was and how he manages to play the same things without screaming "Dull!" or "Boring!" or some other variation - Sherlock hates repetition, but that's what this music is, even if it does have those subtle progressions that John has slowly grown to hear.
John feels strangely and wordlessly grateful to Sherlock for it - this is one more thing he owes Sherlock, and he knows it, even if he'll never say it aloud. He has no idea how Sherlock Holmes, the prickliest, most contrary and self-centered person John has ever met, manages to somehow fix John's broken parts, but he knows, sometimes, that if he hadn't met Sherlock when he had, he would have broken completely and beyond repair.
He could ask what these pieces are if he heard them in the day, but nighttime is a different world; Sherlock plays music that is unlike him and John's mind plays nightmares that leave him unlike himself, and he can't ask. Can't take himself out of the room, can't face anyone or anything, let alone Sherlock - Sherlock may know pretty much everything about John at a glance, and John knows he owes Sherlock more than he can ever put into words, but he also doesn't think he can take Sherlock observing him when he's this naked and raw. He is still broken, and this is only half-fixed and fragile, and Sherlock can only fix the broken parts because he can also shatter John like glass. Too fragile, now, for that double-edged sword with this. He can only lay in bed, heart pounding in his ears, and stare at the ceiling, listening to the strange and haunting music his flatmate plays late in the night.
It's calming and soothing even when it's furiously not, and the piece Sherlock is playing now changes into what must be another movement after a faint pause; into something that is slow, the repetitions taking longer, and almost unearthly beautiful.
He closes his eyes and lets the aching, deceptive repetitiveness lull him back to sleep.
Like the music Sherlock plays in the night always does.
On nights like this, he plays his violin, plays things nothing like he plays during the waking hours.
On nights like this, he wakes with a scream dying unuttered in his throat, feeling a helpless weakness nothing like he feels during the waking hours.
Sherlock tightens and rosins his bow, adjusting his fingers on the frog minutely to its weight, and sits with his violin in rest position on his knee, feeling the strings under his fingers as he thinks.
The strings are familiar and comforting, and fit into the groves in the tips of his fingers that playing for so long has produced. Part of his fingerprints, now, part of him, an identifier. Anyone who observed instead of just seeing could take one look at his left hand and know this part of him. His mind is flipping through sheet music, trying to figure out what to play to distract himself when--
Ah. There it is, then. From earlier patterns, he'd been expecting this, sooner rather than later - John's made the decision for him.
Something by Glass; middle works should do, he thinks, and mentally flips through a new set of sheet music, one he has tucked away in his mind in a place, in a room he hadn't even been aware his mind was creating to file things until he'd mentally all but stumbled upon it, separate from the normal music, until he find what he wants.
He stands up and tucks violin under his chin. The chin rest, too, leaves tell-tale signs under his jaw and on his neck for anyone who knew to look.
Glass takes concentration and focus. It's easy to play Glass, with all those endless arpeggios, but not easy to play him well. He rarely has the patience for Glass anyway; when he's playing to suss out a problem, he prefers not to be endlessly counting - it's distracting, but not in the way he wants. The need to constantly be changing is why he chose the violin. But he's not playing tonight to help him think.
He's playing to help someone else stop.
The sheet music, like so many other things, is tucked away in a tiny corner of his mind palace, in a little room that is nothing like the other rooms he uses as his file system, but is identical to the one John so restlessly sleeps in now. The room where his brain has filed arrangements he has done, nights when he is bored but restlessly waiting, of Glass, of Reich, of Adams; of concertos for piano, for cello, for saxophone, of music from Satyagraha, from The Cage, from Klinghoffer, for a solo violin.
He does not know when his mind created that small room, but he knows it houses more than just arrangements of minimalist music.
It houses what Moriarty would burn to cinders but what Sherlock would burn to the ground himself rather than let Moriarty near any of the sentiment it somehow has come to house as unexpectedly as the music.
Concerto I, he decides, but third movement first, as the faint sounds of distress coming from John's room grow slightly louder, then raises his bow and begins to play.