So I grabbed a service clerk to hold my till, ran upstairs, punched in the keycode for the staff room (for three whole seconds I thought I'd forgotten it; that was fun) and into the bathroom.
Didn't actually vomit, just felt like I was going to. The manager (Kevin) came up to see if I was all right (which was nice) and told me I should go home. So I called Dad, and he came, and here I am.
Great first day though, huh?