Manuel.
I had similar experience od non-dual (non-human) existence. It happened suddenly and was extremely painful and confusing. There was this odd feeling of disapearing from human existence and vanishing into nothingness, beyond of what makes us human and individual.
Later when reading Ramana and Nisargadatta I recognized this state to the letter but they were talking about bliss of non-dual existence and transcending individuality while I felt only mind numbing fear and even physical pain.
Later I've found that there are rare mental "disorders" called derealization and depersonalization experienced among pot and LSD users but also among yoga practicioners triggered by Kundalini awakening. It is not just fleeting sensation, it may stay with you for the rest of your life and incapacitate you in so many ways.
That's when I started to rethink this extreme types of advaita teachings beacuse it is one thing to intelectualy understand or even realize in meditation these concepts and quite another to truly experience them on existential level. To feel what it does to your body and mind and being completely unable to distance from pain.
Many of depersonalization/derealization/Kundalini syndrom suferrers describe states of mind which are commonly regarded among revered hindu advaita gurus and as signs of enlightment. Perhaps some centuries ago if they were born in India these people would be considered enlightened or perhaps in different cultural context these experience would take completely different form. I think that for us it is not relevant beacause we live in one radically different age.
For us ordinary people who want to live our lives in happiness, health, to listen to a good music, have a laugh with our friends and do all the "trivial" thing in a good spirits such practices can be devastating. We are being catapulted out of the world of good and evil into some strange dimension which can be described as prolonged agony of disintegration of subtle bodies. Experience can even be blissful for long time and suddenly turn into hell. I'm thinking a lot about causes of such turns. Perhaps it happens beacause we are not purified, our subconscious and physical is resisting. I'm thinking about Ramana's death experience and finding many similarities but this boy was living simplest of lives, he did not even have dreams.He has no desires even before so called enlightment happened. I think that his normal state before death experience was something many of us will not attain in this lifetime.
There was not much to burned, but we have desires, we have body , brain which will react to mental revolution caused by extreme practice of advaita sadhana.
There was one danish mystic Martinus who warned westerners against eastern practices that force enlightment beacause they can cause serious damage to brain and even subtle bodies.He advised instead to first develop compassion and love toward other beings and follow example of Jesus Christ. To eradicate bad habits of mind and body and not to attempt to eradicate mind itself. First of all we have to become human and being human is much more than we think.
That said, I am not against advaitins such as Nisargadatta or Ramana, and would be happy to see people attain peace with their help but now I can see how their teachings are not completely harmless and natural ( as they claimed many times) for many of our "westerners" who have responsiblilities toward society and our families. They can cause mental disorders in unprepared minds and how many people can honestly say they're prepared?
Perhaps they worked better when minds of people were simple, when ego wasn't so integrated and solid, but now people should be warned before they enter this path.