Mystics belong to very different religions/spiritual groups (Sufi, Christian, Shamanism,...), but also there are individuals as well. Usually, their motivation/goal is to becoming one with God or the Absolute, the aim at the union with the Absolute, the Infinite or God. While they try to reach their goal, they achieve extraordinary consciousness states, some kind of ecstasy or altered state of consciousness, sometimes like drugs.
We desire to reach levels of consciousness that are beyond humans (highest consciousness), like the God of Allconsciousness with absolutes as capabilities within a blissful constant state, without losing individuality (independent) and freedom.