[If he cared about her any less, he might joke about her being worried about him -- instead, he just ends up giving a small shrug, trying to somehow convey the mix of everything.]
Yeah, 'm fine. Just-- it's a long story, I promise I'll tell you all about it sometime.
[He grins at her, then, bright and full of confidence.] Sure you are, but not without good reason. Say, you wouldn't happen to have a lunch break comin' up?