I'd have to say that nihilism has been a product of my depression, which probably isn't the best reason for becoming a nihilist. However, as you've pointed out, this isn't a thread for defending or arguing against the stance.
I just bottle it up alongside most of my feelings, it used to have an ok success rate.
the meaningless of everything gets me down
I know what you mean man, I can switch from being happy to being cold in an instant. The "cold" feeling lingers for far longer than any short-lived moods of happiness.
Anyways, sorry if my non-advice wasn't helpful, but it seems that we both deal with it in a similar way.
And as for how long it will work? It hasn't worked in the last 3 months for me, which have probably been some of the worst. As a last-ditch effort, I'm now trying to ignore reality.