Dean had always expected the nightmares to end once the Apocalypse was over, but they didn't.
If anything things worsened, as since Castiel had become mortal and needed to sleep, Dean could no longer wake to see those quiet blue eyes calmly looking back at him. Now each time he awoke it was to terrible, stifling blackness.
Like the kind that is greeting him now. As Dean wakes from his third nightmare that night, his eyes automatically flicker around to try and catch sight of Cas' intent stare before he realises the angel is no longer awake.
"Dammit, Cas, why're you never here when I need you?"
"What makes you say that?" Cas says calmly, his gravel voice sounding surprisingly sleepy.
Dean yelps. "Jesus Christ, Cas! What have I told you about appearing suddenly?"
Cas laughs and doesn't bother to respond. Despite losing his Grace, the angel has mostly kept the same annoying angel habits as he had before.
Silence settles over the room, but it isn't the oppressive emptiness of before.
"Cas?"
"Hmm?"
"Why are you awake?"
"You could not sleep. After all that we have shared, I don't see why you should be alone in this now."
"Oh." Dean suddenly remembers seeing exhaustion written across the angel's face before now. "Then, the other times too...?"
"Yes."
Dean pauses awkwardly. "Um, well..." He clears his throat. "I mean, thanks."
Cas doesn't seem to mind the fact that Dean has been staring at the carpet the whole time he haltingly thanked him.
"Sleep well, Dean." Cas smiles softly.
And for the first time in weeks, he does.
And a part of him wonders if, just maybe, it was because Cas' small smile crept into his dreams.