Nie Huaisang is, in a word, miserable, which might perhaps excuse his lack of reaction to the sharp rapping at first. He almost mistakes it for the pounding in his head--but then he realizes that the knocking was actually a real sound and not an echo of the effect of his head.

He groans, quietly, before turning his head to look towards the door. After a moment, he pushes himself to sitting, then standing, and starts shuffling towards the door. You know. The place a normal person would assume a knock was coming from.