What kind of sickness is this?

I feel really odd. My stomache is upset, I've been tired but unable to sleep, and nothing is exciting me. Everything anyone sounds me is just like...blah. Normally I have a great sense of humor and i'm quite outgoing, but I just don't...well I don't feel like theres a point to being outgoing or going out of my way to be happy. Is this a sickness or what? PS, i'm not lovesick because I have a girlfriend and can see or talk to her any time night or day and she'd be thrilled just to hear my voice...