A friend of mine recently pointed out to me the linguistic theory of up-down orientation:
Happy is associated with UP - my spirits rose; I'm in top shape; things are looking up; I'm at the height of power; I am an upstanding citizen; I'm at the peak of health.
Sad is associated with DOWN - my spirits sank; I'm down in the dumps; I'm under the weather; things are going downhill; I am under his control; I'm downtrodden.