Dean was stirring in his sleep; fighting away an invisible demon only he could see. Cas sat silently on the edge on the bed, staring out of the window. The sun would be up in a few hours. A few hours and they would be on the road again.
He never knew what to do with himself in between the days. Some nights Dean would sleep for eight full hours. Eight. He used to grow inpatient. Would 'accidentally' make too much noise so that he would wake. Maybe the Impala's alarm system would 'accidentally' be set off.
He slowly learnt over time that the more sleep Dean had, the better he functioned throughout the day; and he needed him to be on alert. Especially alert for the next few days.
He's still stirring but he's only been asleep for about three hours. That's not long enough.
He looks so vulnerable as he sleeps. So fragile. It reminds Cas of Tanya. He remembers the way Nora would sing to her, soothing her into a deep sleep.
He looks over at Dean, his eyebrows pulling together as an idea forms.
Softly he begins to hum and Dean starts to relax. The tension leaving his face.
"Take my love, take my land, take me where I cannot stand."
His baritone voice broke a little as he was tries to sing as softly as possible.
"I don't care, I'm still free. You can't take the sky from me."
Dean's breathing slows and he seemingly falls into a deeper sleep.
"There's no place I can't be since I found Serenity."
Castiel smiles as he can see Dean has finally settled. He turns away from him. Looking out of the window.
Dean's voice makes him jump slightly. "Cas."
"Yes, Dean?" He turns to face him once more.
"Don't you ever. Ever. Do that again."
"Oh." He looks down, a little embarrassed. "Okay, sorry."
"… So creepy." Dean mutters before drifting off to sleep.