Let us imagine, using a common metaphor, that we can geographically describe a positive/happy moment as being "up" and a negative/sad moment as being "down".
Sometimes we go straight up, rocket-like, and glee, and have fun. The logical consequence is that, after a brief plateau period at the top of the parable, we shall descend at least as far down as we went up. Experience suggests that our descent usually will travel further then our ascent, by implying that our ascent begun from a "middle" state of being to a "negative" one.
Empirycal experimentation convinced me that at this point gravity begins to falter and work at it's own leisure. It occurred to me that there is a point in this downward progression in which the mood is fixated in a precise negative level, a sort of "negative plateu" which I'm fond of calling "melancholy". During this period one still might feel as if he's drifting down, but the mood doesn't actually worsen.
I believe that the duration of this "melancholy" is strictly connected to the duration of the ascent, although in an inverse fashon: the faster you go up, the longer you'll "drift".

It only makes sense that each ascent shall be followed by a fall; are optimists fools?
It only makes sense that each descent shall be followed by an ascent; are pessimists fools?

I'm writing this "captain obvious"'s piece of essay down 'cause I need to get it out of my head. I have to go back studying.