This can lead to a situation in which the mystic can abuse the experience, gather power for him- or herself. You can ultimately end up with David Koresh. Further on this point, mysticism can lead to intolerance. Anything worthwhile that a mystic has said, has been said better by a philosopher. This is true because philosophers do not appeal to private experience.
Mysticism can lead to an abandonment of self.
It is a suicide of the person, if not the body. It is irrational to pursue this. The study of mysticism will not lead to mystical experience any more than philosophy of religion will lead to faith.