http://en.wikipedia.org/wiki/Two_truths_doctrine
It's a very nuanced and often misunderstood concept. Leaning too far to either side (hyper-reification of and attachment to the material world on one side, and Śūnyatā ( http://en.wikipedia.org/wiki/Śūnyatā ) -- the emptiness or lack of "thingness" of all concepts -- on the other, lead each to their own problems. Of course, you can get so wrapped up in the observance of walking that line that it becomes a problem, too, which is sort of where Zen steps in with the simple and the absurd.
It all adds up to normality, like you said. I like that.
But life demands, and I stopped my practice and dove back into it with little thought, and that's when things got bad. I had no drive, no motivations, and didn't have a clue who I was anymore. But I also wasn't meditating, which can serve as preventative medicine against the effects of these things in the "real world". I felt kind of clueless and naked, like an amnesiac dumped in the middle of a big city.
Well, anyway, long story short, you'd be surprised how powerful these ancient techniques can be, and you'd be wise to seek guidance from someone experienced before you go dismantling yourself all willy-nilly :). I'm doing wonderfully now, though. And I'm not currently practicing.
You have a world view that you have acquired/formed based on certain assumptions that you may have never questioned. Once you start questioning them, you won't stop at any assumption, and you go into a sort of mental abyss, especially, if you have never believed in God.
One consolation is that however hopeless it may feel when you go there, you'll probably come out and get back to your usual self.
