Thank you for your thoughtful and extensive reply. Whilst I have read up on the subject, the matter is esoteric and widely opinionated online; I was curious on your take and signed up just to ask that question (I didn't realise you replied). I have also largely forgotten about the subject since a long time has passed without anything of note.
And thank you for relating your experience. I have never spoken to anyone directly about this who has also experienced similar.
I will relate my experience just to hone into a point at the end...
I have also experienced a similar feeling to the falling - it feels like my body is vibrating a couple of times a second and the sense of gravity moves around like a pendulum; it even feels like there are multiple gravity wells. If I hang onto this vibration my head gets "sickly"/hot my vision vibrates back and forth and after some time there is break through like an explosion into an altered state of reality where everything looks and feels golden (doing open eyed meditation) and joy and rapture completely envelops my body quelling any negativity like drinking without realising I'm thirsty. Although I have not experienced this state for over a decade now it is still vivid in my memory.
I used to be able to do this almost every meditation session before the "Kundalini" experience. The difference with the "Kundalini" experience was that it persisted outside of meditation which was the frightening thing; it accompanied terror of disappearing and hallucinating fractal patterns as if I'd taken LSD (I've largely forgotten this).
So my understanding is that the first experience is called the first Jhana whilst the second is called "Kundalini awakening". The first experience felt grounding and safe, the second experience felt like descending into madness. I was able to ground myself slowly with metta meditation.
I am far from realised/awakened and certainly there are people much more practiced (and wiser) than me who haven't experienced similar states.
I was experiencing trauma at the time of being able to enter into these experiences and I was using them as an escape from reality. I believe that the trauma was the catalyst and it wouldn't have happened without it...
My current theory is that if one is not sufficiently grounded nor practicing right livelihood, effort and action before delving into these altered states of mind then it may cause an unravelling of the mind. I believe that there is a danger in trying to force these experiences rather than letting them unfold naturally through years of strenuous practice. I believe that there are short-cuts (that I accidentally stumbled into), but they should only be attempted once one has arrived at it naturally.
The Buddha certainty highlighted the benefits of these experiences but they were never meant to be practiced in isolation of all his other teachings. My understanding is that Buddhist texts are generally absent of negative "Kundalini awakening" experiences which leads me to think that it's something that wouldn't naturally arise with correct practice.
Does what I say agree with your thoughts on the matter?
Do you have any personal resources regarding "kundalini awakening"? Specifically regarding permanent changes.
10 years ago I had similar experience in Goenka retreat as you described accompanying hallucinations, vibrations and dissociation (lasting almost a few days afterwards). I rightly left before it become more severe since no one there seemed to have a clue what was happening and were seemingly just following a script. I largely gave up meditation since then, but still practice sporadically, but with no body scans. I've always wondered what mental alterations would have occurred if I continued. Although I have no desire to repeat the experience.
Whilst you specified a 5 minute walk on your criteria I think you should also consider the fact that there is generally very good public transport in London where prices would be cheaper a bit further out. The location is close to several rail stations (Blackfriars, Farringdon), the new Crossrail route (farringdon) opening in a few weeks and tube lines (central, circle, district). With the new cross-rail route it should be possible to access zone 4 locations in 20 minutes.