A common metaphor, probably based on bodily experience. Paired with Down Is Bad.
* Things are looking *up*. * Stocks are *falling!* Oh no! * *Peak* sales come between Thanksgiving and Christmas. * It's been *downhill* ever since.
The experiential basis for this is based on things like:
* When you're sick, you lie down. When you get well, you "rise from your sickbed." (A "down cow" is one that's sick and refuses to get up.) * Dying means going down and *staying* down. * In a fight, being down on the ground is a vulnerable position. * When it comes to a battle, you'd rather be the side up on the hill than the side that has to climb it.