Peak experience is a term used to describe certain transpersonal and ecstatic states, particularly ones tinged with themes of euphoria, harmonization and interconnectedness. Participants characterize these experiences, and the revelations imparted therein, as possessing an ineffably mystical (or overtly religious) quality or essence.
Many of the nuances the term now connotes were expounded by psychologist Abraham Maslow in his 1964 work Religions, Values, and Peak Experiences . To some extent the term represents Maslow's attempt to "naturalize" those experiences which have generally been identified as religious experiences and whose origin has, by implication, been thought of as supernatural. Maslow (1970) believed that the origin, core and essence of every known "high religion" was "the private, lonely, personal illumination, revelation, or ecstasy of some acutely sensitive prophet or seer" (p. 19).
The nature of peak experiences
Peak experiences are described by Maslow as especially joyous and exciting moments in life, involving sudden feelings of intense happiness and well-being, wonder and awe, and possibly also involving an awareness of transcendental unity or knowledge of higher truth (as though perceiving the world from an altered, and often vastly profound and awe-inspiring perspective). They usually come on suddenly and are often inspired by deep meditation, intense feelings of love, exposure to great art or music, or the overwhelming beauty of nature. Peak experiences can also be triggered pharmacologically. A 2006 double-blind clinical study by Griffiths and colleagues showed that psilocybin (the principal psychoactive component of various psychedelic mushroom species) induced intense peak experiences in a majority of study volunteers . In a 14-month follow-up study, a majority of volunteers reported that the psilocybin-induced experience had been overwhelmingly positive and was among the five most personally meaningful spiritual experiences of their lives .
Maslow (1970) describes how the peak experience tends to be uplifting and ego-transcending; it releases creative energies; it affirms the meaning and value of existence; it gives a sense of purpose to the individual; it gives a feeling of integration; it leaves a permanent mark on the individual, evidently changing them for the better. Peak experiences can be therapeutic in that they tend to increase the individual's free will, self-determination, creativity, and empathy. The highest peaks include "feelings of limitless horizons opening up to the vision, the feeling of being simultaneously more powerful and also more helpless than one ever was before, the feeling of great ecstasy and wonder and awe, and the loss of placing in time and space" (1970, p. 164). When peak experiences are especially powerful, the sense of self dissolves into an awareness of a greater unity. Maslow's theories appear to be supported by the recent reports from Griffiths and colleagues, in which community observers (such as close family members) reported a variety of positive personality changes in volunteers in the psilocybin arm of the study.
Maslow claimed that all individuals are capable of peak experiences. Virtually everyone, he suggested, has a number of peak experiences in the course of their life, but often such experiences are taken for granted. In so-called "non-peakers", peak experiences are somehow resisted and suppressed. Maslow argued that peak experiences should be studied and cultivated, so that they can be introduced to those who have never had them or who resist them, providing them a route to achieve personal growth, integration, and fulfillment.
Sustained Peak Experience
Maslow defined  lengthy, willfully induced peak experiences (plateau experiences) as a characteristic of the self-actualized. He described it as a state of witnessing or cognitive blissfulness, the achievement of which requires a lifetime of long and hard effort, and also self-actualization.
"Peak experiences are transient moments of self-actualization" (Maslow, 1971, p. 48).
On peak experiences: "Human beings do not realise the extent to which their own sense of defeat prevents them from doing things they could do perfectly well. The peak experience induces the recognition that your own powers are far greater than you imagined them." - Colin Wilson 
A somewhat more facetious and ironic viewpoint: "We can have in life but one great experience at best, and the secret of life is to reproduce that experience as often as possible." - Oscar Wilde
The term peak experience and peaking are widely used in the drug subculture to describe such states, specifically when induced by the consumption of hallucinogenic drugs, such as LSD, Marijuana, Psilocybin,MDMA, or Mescaline.
Prof. Gad Yair from The Hebrew University has developed a line of research on Key Experiences, especially relating to educational events. His papers on Key experiences in higher education and on the role of those experiences in educational turning points are readily available over the net. The concept of key educational experiences refers to singular, short and intense educational encounters that proved to have strong and long-lasting effects on adults. These encounters are at times associated with a specific person who led them [e.g. teacher, parent, youth leader], at others with the structure of the episode itself [e.g. progress toward a peak event which is then associated with insight and hindsight]. Indeed, many respondents speak of their key educational experiences in terms of sight: Exceptional activities cause prior blinders to be suddenly lifted off, producing clear vision and insight, notably about students’ own selves.
- Maslow, A. (1970). Religion, values and peak experiences. New York: Viking.
- Griffiths RR, Richards WA, McCann U, Jesse R (2006) Psilocybin can occasion mystical-type experiences having substantial and sustained personal meaning and spiritual significance. Psychopharmacology (Berl). 187(3):268-83 PMID 16826400]
- Griffiths R, Richards W, Johnson M, McCann U, Jesse R (2008) Mystical-type experiences occasioned by psilocybin mediate the attribution of personal meaning and spiritual significance 14 months later. J Psychopharmacol. 22(6):621-32. PMID 18593735
- Maslow, A. (1970). Religious Aspects of Peak-Experiences. Personality and Religion. Harper & Row: New York.
- Maslow, A. (1971). The farther reaches of human nature. New York: Viking Press.
- Yair, Gad (2009). "Cinderellas and Ugly Ducklings: Positive Turning Points in Students' educational careers—exploratory evidence and a future agenda" British Educational Research Journal, 35 (3): 351-370. [DOI: 10.1080/01411920802044388]
- Yair, Gad (2008). "Key Educational Experiences and Self-Discovery in Higher Education," Teaching and Teacher Education, 24 (1): 92-103.
- Yair, Gad (2008). "Can we Administer the Scholarship of Teaching? Lessons from Outstanding Professors in Higher Education," Higher Education, 55 (4): 447-459.