Trust him, he's spent enough of his waking time being frustrated with the general nonproductivity this week. Try to draft lesson plans or get some reading done? Doesn't work too well when you're so sleepy you could fall asleep standing up.
"In the dungeons? Heavens..." His tone is softly surprised, sympathetic, but he doesn't really prompt an explanation.
If this is truly a dream, there's little point in continuing to clean. Sebastian never sits down in Ciel's presence, or in Snow White's, or whenever he's working, generally speaking... but since it's just the two of them here, both servants, it's all right for him to take a seat. He sits, opposite her, in one of the other armchairs, but doesn't bother procuring any tea for himself.
"That would be disconcerting, I'm certain. Yet, given the nature of what is happening right now... don't you think any person stumbling into such a dream would direct their concern towards the one having the dream rather than any discomfort of their own?"