I experience brief moments of feeling unreal and like nothing exists. It happens occasionally and comes on suddenly. While this is happening my heart starts pounding and my mind races. Thoughts of "Who, What, Where am I, Am I real, Does anything exist, Is this all a dream?". Then after a couple seconds I snap back into reality. These episodes have been happening for as far back as I can remember. It used to freak me out in school. I am afraid of it being caused by some really bad disease. I've read up some on depersonalization/derealization, but not sure if that's what I'm experiencing.