I had read glowing accounts, written by learned men, of great benefits resulting from concentration, and of the miraculous powers acquired by yogis through such exercises. My heart began to beat wildly, and I found it difficult to bring my attention to the required degree of fixity. After a while, I grew composed and was soon as deep in meditation as before. When completely immersed I again experienced the sensation, but this time, instead of allowing my mind to leave the point where I had fixed it, I maintained a rigidity of attention throughout. The sensation again extended upwards, growing in intensity, and I felt myself wavering; but with a great effort, I kept my attention centered around the lotus. Suddenly, with a roar like that of a waterfall, I felt a stream of liquid light entering my brain through the spinal cord.
Entirely unprepared for such a development, I was completely taken by surprise; but regaining self-control instantaneously, I remained sitting in the same posture, keeping my mind on the point of concentration. The illumination grew brighter and brighter, the roaring louder, I experienced a rocking sensation and then felt myself slipping out of my body, entirely enveloped in a halo of light. It is impossible to describe the experience accurately. I felt the point of consciousness that was myself growing wider, surrounded by waves of light. It grew wider and wider, spreading outward while the body, normally the immediate object of its perception, appeared to have receded into the distance until I became entirely unconscious of it. I was now all consciousness, without any outline, without any idea of a corporeal appendage, without any feeling or sensation coming from the senses, immersed in a sea of light simultaneously conscious and aware of every point, spread out, as it were, in all directions without any barrier or material obstruction. I was no longer myself, or to be more accurate, no longer as I knew myself to be, a small point of awareness confined in a body, but instead was a vast circle of consciousness in which the body was but a point, bathed in light and in a state of exaltation and happiness impossible to describe.
After some time, the duration of which I could not judge, the circle began to narrow down; I felt myself contracting, becoming smaller and smaller, until I again became dimly conscious of the outline of my body, then more clearly; and as I slipped back to my old condition, I became suddenly aware of the noises in the street, felt again my arms and legs and head, and once more became my narrow self in touch with body and surroundings. When I opened my eyes and looked about, I felt a little dazed and bewildered, as if coming back from a strange land completely foreign to me. The sun had risen and was shining full on my face, warm and soothing. I tried to lift my hands, which always rested in my lap, one upon the other, during meditation. My arms felt limp and lifeless. With an effort, I raised them up and stretched them to enable the blood to flow freely. Then I tried to free my legs from the posture in which I was sitting and to place them in a more comfortable position but could not. They were heavy and stiff. With the help of my hands, I freed them and stretched them out, then put my back against the wall, reclining in a position of ease and comfort.
Source: Kundalini the evolutionary energy in man by Gopi Krishna