Angels don’t need to sleep.
Castiel’s not entirely sure he’s all angel.
When he placed his hand on Sam’s brow he felt exhaustion. Of course, he didn’t know what it was at the time. Human sensations for an angel are like colours to a blind man. How can you put blue to its name without someone explicitly telling you it’s so? Placing the two side by side like a children’s picture book? Feelings rush at him, and he knows all the words, in every language, in every galaxy and mode of existence, some long forgotten, some that haven’t been constructed yet, but he doesn’t know what these feelings are called until someone matches the description with the word.
But he’s had a lot of white cold time to think, and he’s figured it out for himself. Sam was exhausted.
There’s no real angel equivalent of exhaustion. It doesn’t translate cleanly. He considers it a composite of the feeling after battle, a great bone ache, and the feeling of giving up. On his brothers, his Father, himself. On Dean. The nearest match to the feeling radiating from Sam’s sticky brow was the narrow ache behind Castiel’s ribs as he fought not to give up on Dean.
He feels a lot like that now, and Lucifer knows.
