다면서

I heard that, is that right?

It raises something you heard about the listener and invites them to confirm it: I heard you won first place, I heard your parents have not been well, I heard you stayed up for days. It expects a yes, so it works both as a friendly opener and as a gentle challenge when the facts do not line up, which is what the line about someone insisting they are not sleepy while nodding off is doing. Add 요 to be polite.

Register: everyday; 요 makes it polite