Disclaimer: Even if I did claim to own Naruto, trust me, I would have no proof to show for it.
It was heartbreaking, but Kakashi never breathed a word about it. He never woke Sasuke from that sleep. It was a strange thing... Sasuke never had nightmares, or even moved around in his sleep at all, whenever Team 7 was on a mission. Kakashi had a theory about that. Probably, it was because sleeping on the ground while on missions made Sasuke unconsciously feel stronger - because he was in Sasuke Uchiha the Avenger Ninja Mode. Whenever Sasuke slept in a soft bed, it was a different story. Maybe it made him feel weaker somehow, or less protected. And Kakashi wondered, did Sasuke ever remember those dreams when he woke? Or maybe that was redundant. The dreams could have been mere memories... and those particular memories, Sasuke would never forget.
So, Kakashi had invited Sasuke to live with him. Nearly a year ago, actually. But back then, Sasuke had declined. Kakashi had always kept the invitation open though, and after one particularly painful mission that had brought those dangerous memories of his to the surface, Sasuke had finally given in to the man's requests.
Now, Sasuke slept in the bed next to Kakashi, but Kakashi himself was wide awake. Moonlight as silver as the hair on his head streamed in through the window to illume the Uchiha, whose rest was obviously being disturbed by nightmares. No one would ever think Sasuke a restless sleeper, but oh he was. The first night it had happened, it had scared Kakashi out of his wits, and he had not known how to react at all. Of course, that had also been not so many days after the incident.... A particular B-rank mission gone horribly wrong, ending with the deaths of those whom Team 7 were supposed to be protecting at the time. Once back in the village, Tsunade had gravely said, "You win some, you lose some," but the three hardened hearts before her had forever lost some of their previous innocence.
Later that same day, Kakashi had gone looking for Sasuke, whom he knew would be a total wreck, and probably hiding, seeing as he hated for people to see him like that. Kakashi had been right. He'd found Sasuke on his own in the woods, sitting under the branches of a tree and staring blankly at the ground. Kakashi had knelt down next to him then. "Want to come live with me?" he asked for the second time. Numbly, Sasuke had nodded. And that night, Kakashi had woken to the sounds of the Uchiha's strangled screaming.
Now, Sasuke was much in the same state that he had been then. Until this student of his had moved in with him, Kakashi had never seen him in such a state. Sure, he'd known that, despite Sasuke's icily stoic attitude, the boy had more rolling emotions within him than probably half the men twice his age would ever understand. Kakashi knew though; he understood, and he had tried his best to take Sasuke under his wing. From this point, it all depended on what Sasuke chose to do....
Still, it burdened Kakashi's heart to know that he could do nothing but sit and watch as Sasuke squirmed and gasped in his sleep. Sometimes, Sasuke would break out into sweat. Sometimes, he would scream. Sometimes, he woke violently, and cried. And Kakashi could never do anything more than hold the raven haired boy close to him, and hope that one day the nightmares would leave him -- that one day, things would all turn out for the best.