I have a book called Kundalini Dream [Walking in the garden of the mind of God], written by Yogin Bhairava, who was my own temporary guide to the sadhanas. Unfortunatley his book appears to be no longer available and I haven't spoken with him in nearly two years. But it's his part biography/part guide to yoga and he goes into insane detail about his growing up in the 60's and taking LSD, which is a gem because much of the literature on Kundalini does not include psychedelics as part of highest tantric yoga.
Here is his telling on Gopi Krsna's first moment of stimulation
"Gaining a resolve to not get distracted this time, his lotus visualization resumed. As the lotus became very lucid in his minds eye, sure enough the sensation at his seat returned, but this time he stayed focused on the lotus.
As he did so, a current of "liquid light"(his words, not mine) began entering his brain through his spinal chord, with a roar like that of a water fall. His body began to tremble as he felt his sense of self consciousness begin to shift out of his body, in a state of exhaltation and happiness impossible to describe.
He became a "consciousness field" that continued to move outwards from his body, while his body awareness diminished and became only a point, while he instead was this vast circle of all pervading consciousness, filling all spatial realty around him, filled with an ectastic pleasure beyond words. In simple terms he moved into and experienced as a conscious experiential state, Sat-Cit-Ananda, the immanance of the "divine Mind", my words, not his.
After thirty minutes or so, the energy that had entered his brain began to retract back down his spine, and he eventually moved back into his original state."
The roaring sound of a waterfall, liquid light, and expanding awareness seem to be very common experiences. Although for me it doesn't sound like water, I assume Gopi Krsna never dropped acid and had nothing else to really compare it to