Castiel wakes, and unconsciously braces himself for pain. That’s what he is used to waking up to, after all. He hasn’t slept very much in his existence. But in his experience, it has always been the wake from forced unconsciousness, the aching of depleted grace, of wounds left unhealed, of scarred wings on his back. Or to the hard floor of the storeroom when he was human, “borrowed” sleeping bag doing little to soften the crick left in his neck all day, or the bruises on his sides and back from the cold concrete.
So waking up without pain, without blood on his face and without a box full of plastic cups jabbing him in the back, it is still unfamiliar, and sets him momentarily on edge. But then there is a soft sigh at his side, and a pair of strong arms pulls him a little bit closer, like they felt him tense up and wanted to squeeze it out of him, and all at once Cas is able to relax and to melt back into the bed.
Because this time, it is a real bed. Because this time, he fell asleep all on his own, exhaustion made only of the normal wear and tear of a day as opposed to the strains of time travel or stolen grace or blood loss. Because this time, he was under the covers with Dean Winchester, who lay quietly breathing next to him, eyes closed and mouth open slackly. Because this time, there were no sharp edges and no pain and no danger looming on the horizon. There was just warmth and peace and a soft mattress beneath him and the love of his life beside him.