I had lots of problems with depersonalization in the past, I think I lived of my life being a mindless helpless doll in the hands of a madman. I never did things consciously, I simply followed my fears and watch myself react to them.
I find that consciously and physically purging my anger on my surroundings help, that punching bag is my new best friend.
I still struggle with derealization though, my brain will simply not believe that my surrounding is real. It's like it was stuck a good 10 years in the past, that's annoying as hell, I find myself poking the walls of the library just to make sure it's real. I also have a great deal remembering where I was last year, although I know I was exactly where I am now. Thinking about it, I feel the same about the other 2 years I lived after the nightmare that was High School ended. I have myself some serious doubts that I ever came out of there alive.