I get it a lot. I will just be walking or sitting in a chair and suddenly it is like I am separate from myself or I will be thinking out loud in my head and the feeling will set in. this totally freaks me out. A lot this happens, that I feel trapped in my own being as myself and that reality is all in my head and I really want to stop existing but there is no escape. This makes things around me feel less real and makes me feel there is something wrong with my thinking and then panic attacks set in every time. This is the most terrifying thing. It is like being in a permanent bad trip.