Agreed with everyone else about the difficulty in expressing it. It's like you brain goes into an operation that it previously thought was impossible, a metaphor would be 'divide by zero', so there's the 'mind-blown by astonishment' feeling. Also, because it is so unusual, it heightens many components of internal awareness as it diminishes the 'noise' from other components. Consciousness takes on an almost alien form, with the ego being dragged along in the passenger seat. A feeling of witnessing something sacred, or even feeling the presence of God can occur as all the top layers of 'reality' get stripped away and at the 'bottom of the hole' as I call it we are left to view the pureness of a zero and one flipping states, and then we realize that's what our entire makeup is formed of, systems of oscillations of systems oscillating, spiraling inwards and outwards from our perspective as far as we can take it.
After a few trips down the rabbit hole we may get good at navigating the inner space, and we may believe that we are communicating with and interacting with another dimension parallel to this world, that the dissociated state may open a conduit through which alien or spirit-based intelligence of pure energy sends us divine transmissions. Jury is out on whether that is real or delusion and we may never really know if there is 'another side' that we can bridge, but we do know that the mind is very complex, and that rational thought would explain it as the mind talking to itself through a glitch in its own matrix so-to-say.