The following is a research paper from 1966 that I came across in Robert Ornstein's 'The Psychology of Consciousness'.
I found it in its entirety here, and I thoroughly recommend reading it all the way through, especially if Psychonautics is something that interests you.
If you've taken LSD, then it's just worth reading anyhow, as it's so interesting looking at the Western take on something so esoteric.
I have edited the research paper to leave you with a couple of points from the first section,
The first section of this article attempts to define and illustrate a specific form of psychedelic experience that is frequently reported when relatively high dosage is administered to normal subjects or selected mental patients in supportive settings. For want of a better term, we have called this form of experience mystical consciousness.
A second section then briefly surveys other forms of altered consciousness associated with the ingestion of these drugs, illustrating how they differ from mystical consciousness.
A third section presents and discusses the research findings that have suggested the similarity, if not the identity, between the psychedelic experience of mystical consciousness and spontaneously occurring experiences recorded in the literature of mysticism A final section considers some of the theological, psychiatric, and societal implications arising out of such research, stressing promise for the future as well as the very definite hazards of irresponsible experimentation.
The form of psychedelic experience here called mystical consciousness can best be described as a dimension of experience that, when expressed on paper by an experimental subject and subsequently content-analyzed, corresponds to nine interrelated categories, each of which is described below.
As Stace has emphasized, such categories attempt to describe the core of a universal psychological experience, free from culturally determined philosophical or theological interpretations. Some of the categories described below are illustrated by excerpts from phenomenological descriptions of psychedelic experiences.
Experience of an undifferentiated unity, we suggest, is the hallmark of mystical consciousness. Such unity may be either internal or external, depending upon whether the subject-object dichotomy transcended is between the usual self and an inner world" within the experiencer, or whether it is between the usual self and the external world of sense impressions outside the experiencer. Both forms of unity are known to occur within the same person, even in the same psychedelic session.
Internal unity reportedly occurs in the following manner: Awareness of all normal sense impressions (visual, auditory, cutaneous, olfactory, gustatory, and kinesthetic) cases, and the empirical ego (i.e., the usual sense of individuality) seems to die or face away while pure consciousness of what is being experienced paradoxically remains and seems to expand as a vast inner world is encountered. A sense of movement is experienced within this inner world through numerous so-called "dimensions of being" towards a goal that is felt to have the status of ultimate reality.
Although awareness of one's empirical ego has ceased, one does not become unconscious.
I found myself grunting in agreement or mumbling, "Of course it has always been this way" over and over again as the panorama of my life seemed to be swept up by this unifying and eternal principle... I seemed to relinquish my life in "layers:" the more I let go, the greater sense of oneness I received. As I approached what I firmly believed to be the point of death, I experienced an ever greater sense of an eternal dimension to life.
In contrast, external unity generally seems to occur as follows: Awareness of one or more particular sense impressions grows in intensity until suddenly the object of perception and the empirical ego simultaneously seem to cease to exist as separate entities, while consciousness seems to transcend subject and object and become impregnated by a profound sense of unity, accompanied by the insight that ultimately "all is One." The subject-object dichotomy transcended may be between the empirical ego and (1) an animate visual object such as another person or a rose, (2) an inanimate visual object such as the leg of a table (Huxley, 1963) or even a grain of sand; or (3) an auditory object such as the music of a symphony.
When looking at the rose as an object, it seemed to "come alive" before my eyes. Its petals seemed to "breathe" as, slowly and gracefully, then unfolded, seeming to express the ultimate in beauty. Fascinated, I watched these movements of "cosmic gentleness" until, suddenly, I knew the rose; that is to say, transcending the dichotomy of subject and object, I somehow became One with the rose, no longer existing as an ego passively viewing an object in its environment. Although in the objectivity of my critical mind, I knew there were no physical changes in the flower, subjectively I seemed to see it in a totally new perspective, a perspective which elicited tears and deep feelings of reverence.... Supporting the ancient monistic school of thought, I expressed the philosophical insight that, 'We are all the same thing."... Another time I commented that, "There is more to beauty than we know."
Read the rest of this beast of a paper, here.