One of Sherlock’s returning nightmares is, that John is gone. And Sherlock is searching him for eternities, he’s walking through the shadows and calls for John, again and again, but he can’t find him, he can’t find him, and suddenly, the shadows try to hold him, he can’t fight them off, and he’s screaming
And he’s suddenly awake, John’s face is above him, full of worry. “Sherlock!”
“John,” Sherlock whispers trembling. “John, you … you were gone … I couldn’t find you …”
“It was only a nightmare, love,” John says and takes him in his arms. Holds him. Rocks him. “Only a nightmare. Everything’s alright. I’m here. I will always be here.”
And Sherlock calms down in John’s arms. He can hear John’s steady breath and his heartbeat, and he knows, it’s real. He won’t be alone again.