Sleep head canon.
I think that Stiles and Derek rarely sleep away from one another. After they get into a committed relationship, move in together, or get married, they only spend the night apart if they have to. Stiles still has trouble sleeping and sometimes has nightmares, and the longer he stays with Derek the more he realizes that Derek has nightmares too. So they don’t like to sleep without one another because each of them knows what to do if the other wakes up from a nightmare , and it’s not so hard to fall back asleep if they wake up beside each other.
They always fall asleep wrapped around one another, touching and finding comfort in each other’s body and warmth. Stiles sprawls out everywhere as he sleeps and Derek is a very contained sleeper, so more often than not Derek wakes up with Stiles sprawled all over him, one leg and one arm on him, or Stiles diagonally laying across him. It annoys Derek at first but he grows used to the feeling of Stiles on top of him when he wakes up. In the mornings where Stiles wakes up before he does, the day is just not as good of a day because Derek feels like he’s waking up on the wrong side of the bed.
Stiles likes the mornings when Derek is half-asleep and nuzzling into his neck and kissing him and growling in his sleep. He likes that Derek lets down his walls and defenses enough to act on Instinct with him, letting his Wolf come to the surface and growling and nuzzling and scenting Stiles when he’s not completely conscious.
Stiles really likes the mornings where he wakes up with Derek slowly stroking his cock or with his cock in Derek’s mouth, or even better the few rare mornings when he wakes up and Derek is slowly pushing into him and Stiles slowly wakes up to the feeling a of being filled and loved.
Derek thought it would be him who stared at Stiles the most when he was sleeping, because Stiles is so beautiful when he sleeps even though he looks kind of ridiculous sometimes. But it’s Stiles who spends too much time staring at Derek when he’s asleep and marveling at how beautiful he is and how much he loves him and how he’s glad that Derek’s safe and surrounded by people who love him.