["Keeping you up too"...? Minato takes that seat willingly (and gratefully, honestly), but he's curious as to what that means. Even exhausted as he is, he picks up on it.]

Oh... yeah, I'm pretty sure I actually can't. [Physically incapable.] I've never really had trouble sleeping before, so...

[...Ah well.]

Is there something else stopping you from sleeping, Elizabeth-san?