Castiel has watched humanity since its creation. He’s not an expert at the internal workings, the emotions and feelings, but he understands the physical part. He’s watched them grow, watched them eat, watched them when they are injured, watched them reproduce, watched them bathe.
When he falls and he’s suddenly human, he doesn’t really consider that he will have to learn about any of those things. He focuses his energy into the mental and emotional aspects that he’s less familiar with, that not even humans themselves seem to understand.
But there’s one physical thing that throws him off a bit.
Cas understands it, of course, why human bodies require rest and what will happen if he doesn’t sleep enough. And actual sleeping isn’t a problem, except for the strange dreams he sometimes has.
The problem is being tired. Those times when he can’t get to sleep right when he would like to- a hunt is keeping him out, or Dean and Sam need him to help research something-his whole mind goes a little fuzzy. His energy drains, and he becomes irritable, unable to control his facial expressions and unhappy sighs.
And then sometimes when he’s tired, it’s not so bad. It’s kind of nice, actually. Like the feeling of being drunk, but knowing he won’t be sick the next day.
It’s one of those nights, when he’s exhausted and buzzing with it, barely in control of himself, that he flops down into Dean’s bed. Dean’s room happened to be the closest, and that’s as good a reason as any, Cas thinks.
“What are you doing?” Dean asks when he finds him.
“Going to sleep,” Cas mumbles, not opening his eyes.
“In my bed?”
And this is the part of being tired that Cas wasn’t prepared for. The part where his brain just forgets to filter his words, and thoughts come spilling out haphazardly, dangerously. “Because your sheets smell good. They smell like you.”
Dean doesn’t say anything, and Cas has the vague awareness that the silence should worry him, but it doesn’t. Cas listens as Dean undresses, blinks his eyes open to find Dean sliding into bed in a t-shirt and underwear.
“Scoot over, at least,” Dean sighs, resigned.
Cas does, but finds himself moving right back, moving into Dean. Dean’s just so warm, a strange combination of hard muscle and soft skin that feels just perfect as Cas snuggles down into it.
“Cas, what the hell?”
“Feels good,” he mumbles, mouth moving against Dean’s neck, and Cas can taste the salt there. “Tastes good, too,” he giggles, flicking his tongue out again to run over Dean’s pulse, which is faster than Cas thinks it should be.
Dean hesitates a moment, then curls into Cas slightly, throwing an arm and a leg over him. “Yeah,” Dean says finally, his voice sounding like he’s just made some sort of decision. “It does feel good.”
Cas lies there for a few moments, strung out and sleep-starved, more open and honest than he’s ever been, and smiles as he has a very Dean-like thought.
Being sleepy is awesome.