"You are kind to be concerned. Thank you." Concerned even for a complete stranger, goodness. Sebastian appreciates it on... some vague, theoretical level. Somewhat. On all other levels he finds it rather annoying, right now.
"But you see, were I to sleep you would not be able to wake me no matter what happens, but for whims of this world. Of that, I am completely convinced." Sebastian breathes a chuckle, but it sounds pretty sardonic. "No person here can fight this world infinitely - it holds us all in the palm of its hand. Once it decides I will sleep, I do not doubt that I shall."
Right now it's definitely still only playing with him and enjoying seeing him struggle. It hurts a little less in the perfectionist pride if he goes down kicking, you see.