Mystical in my opinion has kind of been taken over full-speed ahead with "oneness"...with people describing said experiences or states of mind as being a sense of great peace and clarity highlighted by seeing/realizing your self as "one" with all. It's a drop in the bucket of spiritual, mystical, transcendental, blah blah experiences.
I usually include in the category of mystical experiences a variety of experiences ranging from prophetic dreams to experiences of oneness. But I also tend to sub-divide mystical experiences into two categories: (1) experiences of oneness, and (2) most everything else (which I call makyo). I do that for largely arbitrary reasons, though. It's just that I have until recently been much more interested in experiences of oneness than I have in, say, premonitions.