Your derealisation could be a way for your mind/body to cope with your constant anxiety. Since you say you don't necessarily FEEL anxiety all of the time, perhaps your mind has just grown tired of constantly being on edge & it just kind of separated you from your environment to protect you. Though I don't have any type of dissociative disorder other than depersonalization episodes when I'm going through severe mania, it does happen to me after a very serious panic attack or when something very stressful happens. I just feel like, while everything exists around me, that it is all blank & devoid of any real connection to me.
I hope I was able to help. I hope you feel better soon.