The whole flat was quiet.
It was two o'clock in the morning, anyone who wasn't drunk, high, or insane had already gone to bed. Sherlock, who had been all three of these things at at least one point in his life, was awake. He was sitting at the bottom of the stairs with his eyes half shut, listening.
Anyone who knew the consulting detective knew that he considered sleep unnecessary, that he tended not to sleep much at all. As of late, however, he'd been getting even less sleep then the usual three or four hours per week. He'd taken up this ritual of sitting at the bottom of the stairs and listening ever so carefully, like a watchdog.
Normally what he was listening for made itself known around midnight to two, but he waited all night just in case.
Just in case John cried out in his sleep.
There it was, the faintest murmur that soon grew into an anguished yell. Sherlock's eyes snapped open and with a flick of his wrist he'd grabbed his violin from where it sat leaning against the wall. He propped it up under his chin and lowered the bow to the strings with expert grace.
He'd written John a song, he might never admit it to his face though. Still, he'd written it for him, to play for him whenever his dreams of the war became too much. When he played something soft and almost sad and longing, John's screams would fade and his breath would even out into the peaceful breath of one that slumbers.
Sherlock played the whole song through even though he could hear that John's nightmares had dissipated within the first few measures. He liked to think of John asleep with a small smile on his face, unconsciously listening to the song Sherlock had written for him.
When the song ended he collapsed back onto his perch, letting the violin lay on the floor. His eyes lowered against his will and a yawn broke unbidden through his lips. Lips that then formed a scowl at the weakness of the human form. With no willpower to move to his bed or to the couch, Sherlock simply leaned against the wall. He figured he could rest an hour and wake up before John left for work in the morning.
For once the great detective was wrong.
Hours later John's alarm clock rang out, and the doctor slammed a hand into the snooze button with all the hatred he could muster. Stretching out his leg which had gotten stiff during the night, he rose from his bed to get dressed. He pulled on one of the jumpers that Sherlock always teased him about and a pair of jeans. Then with a yawn he trod down the stairs seeking some form of caffeine.
What he did not expect to find was a consulting detective asleep on the stairs.
"...Sherlock...?" He whispered, mostly to himself as he wasn't sure he wanted to wake the man. He stepped carefully around his flatmate before turning to study him. You didn't need Sherlock's observation skills to know that the detective looked beaten and tired, pale and curled up on the stairway with his violin's bow clutched in one thin hand.
John took a step back, and it was the sound of that footstep that had Sherlock blinking awake. His eyes widened in shock when he realized how late he had allowed himself to sleep, then he yawned casually and leaned forward to set his bow down next to his violin.
"Morning." He rumbled.
"Good morning...?" John tilted his head with a slight chuckle. "Was your bed not good enough?"
"...I ended up here." Sherlock explained vaguely, avoiding eye contact.
"Did you sleepwalk?" John pushed, but he was met by one of Sherlock's mysterious looks.
"No." The detective tried to stand but his limbs had fallen asleep from laying in an awkward position and John had to catch him before he tumbled down the remainder of the stairs.
"Whoa, careful..." John looked concerned, and Sherlock loved to see concern on his friend's face. "Are you alright, Sherlock? Why were you on the stairs. Be honest."
"...No reason...I just heard you cry out." Sherlock muttered, still leaning against the doctor for support while his legs regained feeling.
"Oh." John was well aware of his PTSD wrought nightmares. For awhile he'd worried that he bothered the detective. Could that be it? Was Sherlock trying to say that John made it impossible to sleep?
"I didn't want you to be scared so I came here." Sherlock nodded sleepily. John's eyes fell on the violin and for some reason a melody floated into his mind, something that seemed so familiar but that he couldn't possibly have heard anywhere before.
"You didn't have to do that...wait..." John started to put it all together. Weeks of Sherlock looking even more like hell than he already did. Finding his treasured violin sitting on the stairs all the time as opposed to safely locked in it's case and then there was that strange melody...
"Sherlock have you been here every night?" John asked.
"...Yes." Sherlock admitted.
"Playing violin when I have a nightmare?"
"Yes."
John smiled, all the people in the world that thought Sherlock was a cold calculating robot were dead wrong and only he got to know it.
"Well you still need sleep too." John scooped the detective into his arms, it wasn't hard considering he weighed next to nothing. Then Sherlock to his own room where he deposited him onto the bed and pulled the covers over him. "None of this 'sleep is boring' rubbish either.
Sherlock was fixing John with a peculiar look, as if he couldn't decide whether he enjoyed or was annoyed by having been carried to bed.
"Alright." He finally consented, turning so that his curly haired head lay against the pillow. John turned to leave the room, but a thought struck him. Sherlock had been helping him sleep for the past two or so weeks. He should return the favor. So before he could chicken out, he lay down over top of the covers next to Sherlock and wrapped the younger man in his arms.
Sherlock simply gave a sleepy whimper and pressed up against the doctor, happy to be in his arms.