If you are in a deep meditation, you may have noticed an interesting phenomenon. Initially, it is not easy to stay in a state of clear awareness; you may find yourself either wide awake with racing thoughts or dozing off and falling asleep. It’s like trying to maintain balance on a beam. However, with continuous practice, your perception becomes more acute, making it easier to remain in that particular state of consciousness—the meditative state. 

With persistent practice of mind-watching and body-relaxing, your awareness expands, allowing you to enter a deeper meditative state—or an altered state of consciousness. In this unique state of mind, you could encounter wondrous phenomena: no self, emptiness, unity, oneness, the dissolution of self, boundless consciousness, and so on. These remarkable experiences are collectively known as spiritual or mystical experiences or religious experiences coined by William James, which many mystical experiences are documented in his book, The Varieties of Religious Experience: A Study in Human Nature. 

Here are a few that I have encountered:

During a time in meditation, my breathing initially felt irregular and labored. Soon after, a cooling sensation, like the coolness of mint, started from the surface of my body and gradually spread to my torso, abdomen, heart, and chest, feeling the entire body cool down. It felt somewhat like the cooling process of a person's body after death. 

Just when I thought the experience was about to end, parts of my body started to feel scorching hot, like burning charcoal. My actual body temperature remained normal as I checked. However, the sensation was intense, as if my body were burning on the surface level, then cooling down and turning to ashes with a sense of freshness and emptiness.

When my entire body had metaphorically burned away and turned to emptiness, I felt no sensation unless I moved my body deliberately. I lost the awareness of the boundaries between my body and the environment. The sense of body boundaries disappeared, and my consciousness expanded, blending with the surrounding environment. Although I knew my body existed in a particular physical form, I felt nothing but emptiness and pure awareness.

I was lying on my bed, feeling the room, the bed, and everything within my awareness was part of me. I felt like the table and chairs were within my consciousness and part of “me” or “self.” It is like “I” filled the room and the entire universe. I was everything, omnipresent, boundless consciousness. I was everything, infinitely large and infinitely small, both presence and absence. I was not a form, not a physical body, but a pure existence. This didn’t mean I could move objects with my mind, but my consciousness felt boundless, united with everything around me, resulting in a sense of oneness.

This particular experience occurred again a few years later when I participated in a 5-day silent retreat in the Bay Area. 

On another occasion, in an altered state of consciousness, my brain raced and urged me to explain things. However, when my sister, Jen, reminded me, "Quiet your mind, stop talking, and listen." Though I was reluctant at the moment, or rather my brain was reluctant, feeling irritated being interrupted and asked to shut up. However, when I stopped my mind and started to listen, I felt as if I had pierced a thin transparent film, leaping from one world into another, as if from the human realm into a celestial one. Of course, it wasn’t an actual celestial world I entered, but the difference felt as stark as the gap between heaven and earth.

During this particular experience, I found it incomprehensible. I couldn’t quite grasp what I had gone through or what exactly happened. In the following months, my thinking and behavior patterns did not seem to change drastically. 

However, as I continued to go through rigorous self-analysis and cleared residual unwanted thoughts and feelings. During an eye movement session with the help of my mom, I began to feel my "self" dissolve—a subtle yet vivid feeling. Over the next few months, I observed a tremendous shift in how I think and perceive. Something unlike anything I had ever experienced before. It felt like a rocket lifting off the ground and entering a new orbit—a newfound certainty as I entered a completely new paradigm.

This was not just another provisional spiritual experience but something that permanently shifted my way of thinking and perspectives. I used to think more linearly while awake, but now it feels as though the meditative state is seeping into the waking state. The two states, once like oil floating on water with a distinctive boundary, are now starting to blend and blur the fine line between them.

In deep meditation or an altered state of consciousness, many, including myself, are amazed by the profound healing effect and metaphysical insight. I’m not entirely sure what happened in my brain, but it somehow changed the course of my cognitive function. However, it is not limited to deep meditation or altered states of consciousness; hypnotic trance, deep and silent prayer, or ritualistic music and dance could also lead to profound experiences.

Spiritual experiences are profound and transformative, not easily achieved, and often happen randomly. Therefore, they are cloaked in mystery and made sacred. However, they are not inherently sacred, holy, mysterious, or religious but rather a natural phenomenon of the brain.

How do spiritual experiences occur? The details of the mechanism remain unclear. Perhaps they involve alterations in brain activities, activating or inhibiting specific brain regions. For instance, the brain constructs the concept of an object by producing ideas of boundaries, color, shape, space, and position. An apple, for example, has a red color, specific weight and shape when held in your hand, and a waxy texture on its skin, but those attributes are generated by the brain.

A brain region, primarily the parietal lobe, is responsible for recognizing physical space. If the activity of this region is inhibited, one might lose the sense of spatial boundaries and orientation, making it difficult to judge the distance between an apple and your hand. Various studies also suggest that electrical stimulation of brain regions in the temporal and parietal lobes can potentially induce out-of-body experiences (OBEs), creating a temporary sense of separation as perceiving the self and body as being in different locations. This might be similar to near-death experiences, where stressful physical situations alter or suppress brain activities. Thus, mystical or spiritual experiences are essentially brain phenomena occurring in specific operational modes, nothing mysterious.

A study published in Nature describes the repeated induction of this experience by focal electrical stimulation of the brain's right angular gyrus in a patient who was undergoing evaluation for epilepsy treatment. Stimulation at this site also elicited illusory transformations of the patient's arm and legs (complex somatosensory responses) and whole-body displacements (vestibular responses), indicating that out-of-body experiences may reflect a failure by the brain to integrate complex somatosensory and vestibular information.

Anesthesia alters how the brain perceives the sensation of pain or puts the brain into a sleep-like state. Similarly, an altered state of consciousness changes our perception, toppling conventional senses and crumbling taken-for-granted realities, bringing us profound metaphysical insights.

However, an altered state of consciousness, like a dream state or general anesthesia, is fleeting. At the moment, it brings incredible healing effects and insights, but once the moment passes, these insights fade into distant memories. Once out of the altered state of consciousness, the brain slowly resumes its previous mode of operation, reverting to its original operating system, Mind OS 1.0, and returning to habitual thinking patterns.

As U.G. Krishnamurti mentioned in the book "The Natural State": 

“I practiced yoga, meditated, studied everything. I experienced every kind of experience mentioned in the books—samadhi, super-samadhi, nirvana-samadhi, everything. But I think that the mind can create any experience you want—bliss, joy, ecstasy, dissolution into nothingness—all kinds of experiences. So it cannot be real, no matter what experience you have, because I am still the same person, mechanically doing the same things. Meditation meant nothing to me, and it didn’t take me anywhere.”

Similarly, Jed McKenna, in his book "Spiritual Warfare," described spiritual experiences as:

“My former bond broker had over thirty direct experiences with the mind of God, but today he’s just an ordinary guy... So as I see it, if this state can’t be sustained, then it’s worth nothing; it’s just another amusement in the amusement park of illusion.”

A spiritual experience is a double-edged sword. It temporarily frees us from conditioning and reveals a reality obscured by the dark cloud. However, it can also lead many to mistakenly believe they have arrived or completed the journey, stopping short of true awakening. They may wind up dwelling at the abstract metaphysical level instead of continuing onward.

Spiritual experience and awakening share very similar characteristics. However, awakening or Enlightenment is a permanent state instead of a fleeting state. Achieving spiritual experience through effort, deep meditation, or whatever action, but awakening is back to your natural state, an effortless movement. Thus, many spiritual practitioners have mistaken the two. 

Spiritual experiences could shatter conventional beliefs, turning one's reality upside down, but profound insights can also lead to arrogance and complacency, causing stagnation or regression. Spiritual experience is just part of the healing and awakening process, not the destination. Therefore, don’t linger, don’t delay, don’t stop, and don’t be deceived. Just keep moving forward!