I'm doing horrendous sir, you?

I walked in to the office at lunch time. A well-dressed man, whom I have never seen in my life recognized me as being someone also over the age of 14. He smiled and with a friendly greeting said, "Hello. How are you doing today?"

I was doing horrible. I got sick. I can't remember a time where I have felt much worse. I was actually walking by him to head to the bathroom to see if I should vomit and go home, or if I could teach my last two classes.

I said, "okay."

Which leads me to wonder if we should limit our greetings to strangers and acquaintances to comments like, "Good afternoon."