Hang on in there, "trying to get better". For me derealisation occurs gradually during the day, getting to it's climax in the evening. For me it starts when I start questioning and doubting in everything. And as bad as it gets, as far as it can go, I always come back more or less wether its a couple of hours later or the day after. To reassure myself I've picked someone I trust, not too far from me, and told myself if I ever go so mad I can't think for myself anymore, I'll put all my trust in that person to guide me.
Also, even if it seems hard or impossible, I try to occupy myself with the things I usually that requires a certain ammount of concentration so I wont think so much about the stuff that debilitates me. I can't keep my mind off the bad thoughts constantly, but at least that way, every day when I go to sleep, instead of having shoveled only bad stuff in my mind all day, half of it is good half of it is bad. So going like this it seems like everyday I have a bit less of thenegative thoughts floating around. I'd say that today compare to the beggining of the week, where I had 99% bad thoughts, I might have had 65% bad thoughts VS 35% normal thoughts.
Of course that alone doesn't do it, I also take low dose of Ativan to keep anxiety down. But it still doesn't keep me from thinking. So I try to avoid negative thoughts for now, until I feel balanced enough to confront them again. Maybe make a movie or write something about it one day!
And one last thing, everytime bad derealisation happens, when it's kind of over, I take the time to notice how nothing has changed around, and I'm still myself . Still have the same memories, people around me are still the same, still like and dislike certain things. The world keeps on turning, your heart keeps on beeting, you are still yourself. It just takes a bit of time.
I hope I can make you feel less alone in this, as I once thought before finding this place. Things change, and when you've been through the worst, it can only start getting better.