Great thread tessa, and as a woman, I understand exactly what you mean.
But as John Grey, author of Men are from Mars Women are from Venus says, and I agree with him completely on this, "I'm fine" is different for men and women.
When a man says "I'm fine" means he's fine; he's ok, there's not problem.
But when a woman says it, it can mean you've made me angry; you've hurt me; you've upset me; don't speak to me right now or I'll bit your head off, but rarely does it actually mean she really is "fine".