On some occasions where I feel irritated/angry/frustrated and/or feeling downright insane on the inside, I can draw a really intense looking Sephiroth while blasting "One Winged Angel" on my iPod or from iTunes. On mellower days I can draw a standard cold and unemotional looking Sephiroth. (Yeah...he's my favorite art muse). I tend to internalize my feelings a lot (sort of a trait for being an introvert) so drawing helps me to deal with coming into terms with those emotions. ...At the least drawing Sephiroth helps me to avoid becoming like him.
If I'm busy with finals or other kind of school work, it leaves me little time to draw. If I do manage to take some time to work on something in PhotoShop or in my sketchbook, I usually do fine. However, sometimes I might be out of it because of being so busy with other work.
I think it works the other way around. For me, anyway Anything, from my domestic/global travels to my nights at the opera to my conversations with people to my favorite books, inspires my art, which in turn, influences my mood when I look back to see what I did.