How did I turn into such a weird freak?

As a child I was a high achieving, happy person. As a teen I was a self-conscious, worried, self-loathing wannabe. Now as a young adult I am a reclusive, megalomaniac, still self-loathing, marijuana enthusiast. How did it get this way? Give me your theories please. Will give best answer. Just give me your best theory on how a person can go from happy and idealistic to a trainwreck of nerves and doubt.