[sohailk]

The "How are you?" question is a way of setting the context of the conversation quickly. Most of the time, everything's okay ("I'm good, what's up with you?"). But sometimes it's not and the "How are you?" question gives you an opportunity to express that it's not: ("Man, I'm feeling pretty crappy right now").

[kbp]

I'd say that depends a lot on who you're talking to. I would answer like that to a close friend, but for most people I know I'd never answer more negatively than something like "eh, kinda stressed, but it's ok", and for a complete stranger (like krzyk mentioned) I would only ever say "fine" or a synonym.