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Sherlock has nightmares, John realizes when he stumbles upon a sleeping Sherlock on a Thursday night. Sherlock has his eyes closed but it is the only thing that hints at his sleepiness, his movements abrupt and the sounds coming out of his mouth are not ones of pleasure. Sometimes, a word escapes between the moans, "no", "don't", "JOHN!" and the call of his name is all it takes for John to take matters into his own hands. He steps closer and calls out his friend's name, careful not to touch him. Sherlock wakes after the third call. He opens his eyes and looks confused, looking at John with narrowed eyes and thin lips.
"John? What -" he starts to say but cuts himself off, choosing to deduce instead.
"Oh, I see." He sits up, rubs at his eyes to erase the sleepiness before sending John a stern look.
"You okay?" John asks in a soft voice, although he already knows how he's going to answer.
"Yes, I am perfectly alright John. Go to bed, you will need sleep for tomorrow's day at work," he states in a monotone tone before standing up and entering the bathroom. The door closes behind him, leaving John staring at it with concern. He sighs but leaves for his own bed.
*
On the morning, Sherlock pretends like nothing happened so John decides to not mention it, but it is in the corner of his mind for the remainder of the day, and he's on his guard the next days, watching Sherlock with care. But John doesn't catch him asleep for a whole week, and he's getting worried.
"Sherlock, have you been sleeping at all?"
"Of course I have," he answers, "but I need to focus on - on this!" He points at his most recent experiment. John's eyes fall on Sherlock's pale skin and the bags under his eyes.
Sometimes, incoherent things come out of his mouth and he stares at nothing for minutes.
"It's not that unusual for him," Greg tells him when John confesses his worries.
"I know, but -" he sighs, "ever since he came back, he's been different."
At one point that night, twelve days after John first caught him, he hears groans that are almost imperciptible if you don't look for them. He comes down the stairs two steps at a time and knows Sherlock is deeply asleep when he sees him trashing his sheets everywhere.
"Sherlock, it's okay, you're fine, we're fine! Sherlock!"
He's panting and gasping now, his hands grabbing his sheet. John can barely see the oultine of his face in the dark but he notices right away when blue eyes catch his gaze. There are tears falling down his cheeks, but John doesn't think he's noticed.
"It's okay, we're safe," he sits on the edge of the bed, not sure if it's wise to touch him yet. But Sherlock's hand grabs his shirt and squeezes, as if to make sure John is real.
"Come here," he takes Sherlock in his arms, stroking his back and passing his fingers in the dark-haired curls. He can feel Sherlock's hot breath on his neck, and from time to time, a tear falls on his shoulder.
After a while, Sherlock's breath evens out and John lies him back down and gets up from the bed. He's turned his back when Sherlock whispers his name. He turns around and sees that his friend is still asleep. He swallows, weights the pros and cons and gets under the cover next to Sherlock. He only means to touch his wrist as a reminder that he is here, but Sherlock catches his hand and locks their fingers together, making John's arm curve around Sherlock's waist. He falls asleep thinking that this is nice.
*
Sherlock is already gone when John wakes up. If John hadn't woken up in Sherlock's bed with dried tears on his shirt, he'd have thought it was all a dream. John pretends it didn't too, or at least he doesn't talk about it when he meets the detective as he leaves the flat. But as he goes to bed that night, he is surprised to feel the bed dipping as someone settles next to him. They don't talk, don't meet each other's gaze, John being on his side, his back to Sherlock. After ten minutes, Sherlock's mouth rests on John's shoulder blades, his chest resting against John's back. He's surprised that he doesn't tense. Instead, he quickly drifts into sleep and he sleeps better than he has in months.
It becomes something of a habit, although they never really speak about it. Until they do, and their relationship takes a turn - for better or worse.