Robin doesn't sleep much himself (if the writing on his wall is any indication). He sometimes lies awake for hours at a time, scribbling numbly on the wall, as if instructing himself to "go to sleep go to sleep go to sleep" will actually make it happen. He hates that he has to sleep. He hates that he's so exhausted all the time, mentally more than physically. He hates that when he tries, he's visited by nightmares and ghosts and things that will not let him rest for long.

But every once in a while, he does sleep. Very rarely, he passes straight through his dreams and into a world of blissful unfeelingness. He passes out, practically unconscious, and sleeps for hours and hours at a time. It's nearly impossible to wake him up when he's like that, which is why Euri's crawling into bed barely makes him budge. He's out like a light.

Sometime after she settles down, he wraps his arm around her and pulls her a little closer to him--probably a habit, might as well be engrained in muscle memory. He always sleeps better when there's someone with him. Maybe it's the conduit of energy, maybe it's something more subtle. But she's warm, and that's all he needs to fall back into a deep level of unawareness.