I had it for a long time. It felt like being a couple of feet off the ground looking through a dim window. It went away when the anxiety went away. I still go though it at times when I have a lot of stress. It feels a little different now. Like a void feeling. It's hard to explain. I just float through it now until it goes away.
Are you on an anti-depressant? They can also cause the depersonalization symptoms.