A common metaphorical system asserts that "up" is the direction of goodness and "down" the direction of badness.
In their *Metaphors We Live By 
*, Lakoff and Johnson, make much of how, generally speaking, we humans think of UP as GOOD. That's probably driven by our experience as bodies in the world
* Plants and people start small and grow up toward the sky to reach their natural state.
* When people get sick, they lie down to recover.
* When they get better, they rise from their sickbed.
* Unless they never rise – because they're dead. Being dead is bad.
So UP is GOOD is one of those pervasive metaphors. It's used to describe mental states as well as physical:
* We say someone has "finally grown up" not to refer to their body but their mind.
* A person's ideas can "soar like an eagle's".
* People brag of having built the tallest building in a city, but not about building the widest building.