I've heard about people awakening their kundalini with that. It fucked them for years since they had no clue what was happening, and no preparation or support.
Extraordinary sensitivity, internally and externally. It's considered a very advanced practice because without a trained mind it is extremely jarring, will induce anxiety and maybe make you start thinking that you have psychic abilities (or schizophrenia).
No, they were very aware of it. Huge energy surges, hallucinations, emotions go haywire, etc. It can take years to stabilise if you don't know what you're doing, and apparently you can easily question your sanity (even if you know what to expect - if you have no guide you might really struggle with understanding the process).
One guy would nearly pass out every time he got an erection, some people have a phase of not being able to eat anything but yoghurt or milk, etc. Huge changes, like a second puberty.
