In truth, it was very tempting to just be put to sleep. He was concerned that he would fall asleep in the middle of something when he was busy throughout the day. And he didn't want to keep Xavier up all night with his own thoughts and nightmares.
He opened his mouth to say no, as a gut reaction, but changed his mind. "Alright." It wasn't that he wanted this, but staying awake all night was not appealing.