Mystical apparently derives from mystery which, in turn, derives from the Greek mysterion, via the Latin mysterium ... methinks. It has too many meanings! The theological one suggests that some knowledge is obtainable only through revelation (rather than through observation and logic) and that such knowledge cannot be fully comprehended. There are others, including what I would term "woo-woo" mysticism which is all about funny feelings and wild imaginations and even peyote-induced hallucinations.