I know that this is a really old post.. But how are you guys doing with this? I've been struggling with these thoughts for a few months and they're crippling. Any coping strategies?
Well actually, things have gotten a little better.
To whoever said it's not the same thing as depersonalization... the thoughts about existence themselves aren't the same thing, but for me at least I definitely get depersonalization, often at the same time. It will go something like "Hmm, why am I myself? Why am I living in this world?" And then after obsessing over those questions for a few minutes, I'll start to feel detached from my body, start to feel like I'm not in control of my body. I feel very dreamy and sort of "floaty" like my soul could just float away from my body at any moment and there is nothing holding me in this world. It feels kind of like gravity just stopped working, only instead of gravity pulling my body to earth, it was keeping my consciousness linked with my body.
I still have anxiety sometimes, and recently (last month) I've had more panic attacks again. I've had these feelings, that I've come to know are depersonalization and derealization, occasionally, but not as much as when I posted before (early 2013).
One of the best coping strategies for me was and still is to just change activities, especially to something where you were going outside and hanging out with someone and doing something new. Try to do something that is thought provoking and gives you some new things to think about.
If that doesn't appeal, some routine things can help as well... moderate exercise (but not too much), meditation, making lists of things to do, cleaning your room, cooking your own healthy food, and just general things to remember to take care of your physical health. I think these things work by reducing anxiety levels overall and increasing energy levels. If you start to feel overwhelmed, take a break from whatever you're doing, check your list of things you need to do, and pick something else. Or just go outside for a walk.
Finally, try to remember that these feelings are -just- caused by anxiety. They aren't philosophical revelations and you aren't any closer to true reality or anything. Plenty of other people can think about life and the universe and "Isn't it weird that we're all just animals sitting on a planet in space?" without freaking out at all. It only freaks us out because we already have too much unconscious anxiety built up already and this is how it manifests itself.