According to Lang and Thalbourne, "the intensity of mystical experiences forms a progression that starts with quite general experiences of happiness, followed by enlightenment by a higher power, and ultimately leading to union with the Absolute." 
"...the intensity can range from a few moments of rapture to several hours of shattering psychological experience."
Timothy Leary recounts a short duration, high intensity connection experience induced by Dimethyltryptamine. "Last fall a minister and his wife, as part of a courageous and dedicated pursuit of illumination, took a psychedelic biochemical called dimethyltryptamine. This wondrous alkaloid (which closely approximates serotonin, the natural "lubricant" of our higher nervous system) produces the most intense psychedelic effect of any sacramental food or drug. In 25 minutes (about the duration of the average sermon), you are whirled through the energy dance, the cosmic process, at the highest psychedelic speed. The 25 minutes are sensed as lasting for a second and for a billion-year Kalpa. After the session, the minister complained that the experience, although shattering and revelatory, was disappointing because it was "content free"-so physical, so unfamiliar, so scientific, like being beamed through microscopic panoramas, like being oscillated through cellular functions at radar acceleration."
Types of experience, from least to most intensive, Insights/intuitive glimmers, Peak Experience, Mystical Glimpse, Mystical Visions, Revelations, transcendent experiences, permanent unions.
- Lange, Rense, and Michael A. Thalbourne. "The Rasch Scaling of Mystical Experiences: Construct Validity and Correlates of the Mystical Experience Scale (Mes)." The International Journal for the Psychology of Religion 17 2 (2007): 130.
- Allman, Lorraine S., Olivia de la Rocha, David N. Elkins, and Robert S. Weathers. “Psychotherapists’ Attitudes toward Clients Reporting Mystical Experiences.” Psychotherapy: Theory, Research, Practice, Training 29, no. 4 (Win 1992): 565.
- Bender, Courtney. The New Metaphysicals: Spirituality and the American Religious Imagination. Chicago: University of Chicago Press, 2010. p. 71.
- Leary, T. “The Religious Experience: Its Production and Interpretation.” Journal of Psychoactive Drugs 3, no. 1 (1970): 76–86. https://doi.org/10.1080/02791072.1970.10471364. p. 342