I don't get Shakespeare stuck in my head often, but he's there now.

I have of late, but wherefore I know not, lost all my mirth, forgone all custom of exercises: and indeed it goes so heavily with my disposition, that this goodly frame the earth, seems to me a sterile promontory, this most excellent canopy the air, look you, this brave o’erhanging firmament, this majestical roof fretted with golden fire, why, it appeareth nothing to me but a foul and pestilent congregation of vapours…

What a piece of work is a man, how noble in reason, how infinite in faculties, in form and moving how express and admirable, in action how like an angel, in apprehension how like a god: the beauty of the world, the paragon of animals; and yet to me, what is this quintessence of dust?

HAMLET, II,ii

The musical version in Hair is good too. And no, I'm not that bummed out (though some Shakespeare scholars believe those lines to be optimistic in nature- I tend to think that someone who has lost all their mirth is not feeling optimistic, at least at that moment).