Captain Swan Headcanon
Killian hogs the bed. He sleeps all over the place, spread out over every available inch of mattress, if he's alone. If Emma's in the bed with him though, instead of spreading out he curls in, tries to wrap his body around hers in any way possible.
And it's annoying because usually Emma doesn't even like to cuddle when she's going to sleep, she prefers to have a little space (and cooler sheets) but the thing is Killian doesn't seem at all aware he's doing it and something about that kind of, well - it tugs at her a little, makes her sigh and let him wrap his arms around her and tangle his legs in hers and breathe on her neck. And maybe she even curls a little closer herself. Maybe she smiles.
They both have nightmares on a fairly regular basis, still. But it's less often since they've started sleeping like this.