Hi bluecanary, I know exactly how you feel. It's unfortunate you are suffering in the same way I am (and I'm sure many others are, too), but it's actually a relief to me to know I'm not alone. When you say you feel like you've cracked the code you weren't supposed to... god, that has been one of my biggest fears. I've never worded it like you did, but I've been terribly afraid that I've had some great insight into the nature of existence that no one else realizes. When I have that thought it causes great anxiety, because I think, "Wait, I haven't had some great insight, but I feel like I have... is this a delusion? Am I becoming psychotic/schizophrenic? Oh no!" Of course we are not psychotic, but I just wanted to illustrate my anxiety because of how easily my thoughts can spiral out of control.
I know how you feel. I have had the same thoughts, and they have bothered me just like they bother you. They come and go and come and go. It's irritating because just when you think you are getting better, surprise! Please know that you are not alone. I have lost many hours of my life ruminating on who I am, who the "I" is. I once felt like I had seen past my ego/personality and realized that there is no one there, that I am just a biological machine and so is everyone else. I never believed that, but it's how I felt, and those thoughts plagued me with severe anxiety for months. I'm not even close to recovered yet, but I have seen great improvement lately because of something I learned...
You are not the individual you once thought you were. You are part of an ecosystem. You are a beautiful, magnificently complex extension of an organic symphony. You were not born into this world, but were born out of it. It is you, and you are it. Just as a wave is a wave, it is also part of the ocean. You are you, but you are also part of the universe. You are the universe experiencing itself, and so am I. Lately, it has helped me immensely to have something to identify with. I am not in this world, I am part of this world. It's beautiful and absurd at the same time. I can identify with the Earth now, with the stars and the trees and the sea. I feel some sort of attachment to it all, and it's comforting. It's comforting to know that I am part of a wonderful, harmonic system of life and fruition. Suddenly, death does not scare me, because I will not die, in some sense. I'm just a wave of the universe (Literally! Your body is made of atoms from exploding stars!), which existed before me and will exist after me. The only purpose of life is to live in harmony with nature, since, after all, we are nature.
I learned this from a philosopher named Alan Watts. My DP has weakened quite a bit lately, and the world is starting to make sense in a way it never did before. My life has definitely been changed. I will recover, but I will never be the same person I was. I will be much wiser and much happier, I think. Well, maybe just happier! Is this enlightenment? I don't know, probably not, but I don't really care. I have no goal of becoming enlightened, I just want to feel better and help others feel better.
I've rambled long enough... hopefully something I said will help you. Remember, we are on this journey together.