There was something about Sam and Dean Winchester that they didn't understand. The two brothers never had nightmares. It didn't really make sense to them. Sure, they'd happen occasionally, but it was rare. And with everything they had been through, they both expected that sleep would be one never ending nightmare, but it wasn't.
It wasn't a hunter thing, either. Mary was plagued by nightmares, and Dean could vividly remember a number of nights where he had woken up to the sound of his Dad screaming in his sleep. Whenever the boys came in contact with other hunters, nightmares were a constant thing. It was impossible not to have them, with all the death and gore you witnessed.
And yet, the Winchesters, who had seen more horrors then anyone else, remained nearly nightmare free.
It took them years to put the pieces together.
Dean's first nightmare in years happened after the angels fell- when Cas had become human. The angel was who knows where, and Dean was wracked with guilt, that he didn't know how to help Cas, that Sam was unknowingly possessed by an angel and Dean had tricked him into it, that the angels had fallen, and that they had failed to close the gates of hell.
The nightmare had been awful. A panic room full of his memories of hell, a dream of torture, or reliving all the death, of every time Sam or Cas had been hurt, of the death of everyone he had lost- of enemies coming back from the dead just to haunt and torture him and the ones he loved.
Dean had woken up in a cold sweat, shaking like a leaf. He had never had a nightmare that bad. His phone had buzzed a minute later with a message from Cas.
I'm sorry.
Dean still has no idea what Cas was apologizing for.
The nightmares had continued, but Dean didn't bother saying anything. He knew Sam knew about them, especially when they were on hunts and shared a hotel room. But Sam knew better then to ask.
Sometimes they would fade away, but then a nightmare twice as bad would happen. Dean had no idea what was plaguing him.
And then, all of a sudden, around the time that Cas got his grace back, the nightmares stopped. Stopped as quickly as they had started.
They didn't start again until Cas died. But they stopped as soon as he came back.
It was only after Cas came back after being killed by Lucifer that Dean got a theory about what was happening.
"Cas," he asked one day. "Can angels stop nightmares?" Cas had frozen.
"...Yes." He admitted, looking Dean in the eye. "We can manipulate human's dreams, to an extent."
"Are you the reason Sam and I don't have nightmares?" Cas tilted his head.
"I have no idea why Sam does not experience nightmares." He said honestly. "But... yes, I have been known to have stopped your nightmares."
"So that's why whenever you lose your powers, or you die, they come back."
"I suppose. I've been trying to find a way to rid you of them permanently, but nothing seems to be working."
"Why?"
"Why what?"
"Why are you stopping my nightmares?" Cas shuffled his feet.
"I just thought," he began. "that you experience so much bad while you're awake, you shouldn't have to experience any while you sleep." Dean half smiled.
"Well, uh....Thanks, Cas." Cas nodded.
"Of course."
That night, Cas wandered the bunker, as he usually did while the Winchesters slept, and he stopped at the sight of someone creeping out of Sam's room.
"He have a nightmare?" Cas asked.
"Not anymore." Gabriel insisted, grinning at his brother.