Derealization happens when you're too anxious, I think. I experienced derealization and depersonalization at the height of my clinical depression and generalized anxiety disorder a decade or so ago. I had both for a whole year (depersonalization and derealization). Half of me felt like I wasn't real, and another half was convinced I was going mad. It took a while before I felt like myself again. As for the depression and GAD, it took me four years to battle and win over those.
Hang in there.