Korean keeps a separate word for each face that sleep has.
나비잠, nabijam, butterfly sleep: an infant on its back with both arms flung up past its head.
노루잠, norujam, deer sleep: the kind you keep startling out of.
그루잠, geurujam, stump sleep: the sleep that grows back after you have already woken, the way a cut stalk does.
겉잠, a sleep that never got below the surface. 통잠, a whole one, straight through till morning. 꽃잠, flower sleep — deep, and sweet.
To name sleep this finely somebody had to have spent a great deal of time watching other people do it. A baby's. An old person's. A sick person's.
Six words, and five of them are about not sleeping well.