I have had these experiences; two prior to psychoactive chemicals. The first two are part of the warp and weave of who I am.
Have studied these experiences across time and place to try to understand. They are ineffable and attempts to explain them are filter through culture, time and life experience. I have written this in another piece I have done:
SPECULATION ON FINDING UNITY (the ‘oceanic’ or ‘one with the univese’ experience.
The brain has a stimulus range. It is the experiences outside this range that are the pathways to the white light. The existence of a stimulation range can be seen various ways the shifts occur.
One path is the through meditation or fasting or sensory deprivation or depression. This is the “too little” end of the range. The brain needs a level of stimulation to keep it from “eating on itself”. When low input of stimulation opens the underlying processes to accessibility.
When the brain receives too much stimulation in the form of whirling dervish dancing or continual sexual stimulation or psychoactive drugs or depression then it overloads and lets go of its control. Here the epiphany explodes into experience.
Notice I have put depression in both the low and the high input. There is the depression that is the “dark night of the soul” where existence shrinks to a point of nonexistence. There is also a depression that it is an overwhelming brain chatter. Both of these occur under perceived duress and with the loss of the ability to use earlier adaptations successfully to manage the duress.
Each person’s range is unique to them as well as to their experience at the particular time. The experience of the shift can be a conscious quest or an involuntary eruption bypassing the controls of the existent worldview.