When I was about 19 years old, I broke up with my first serious girl friend and had a bit of a breakdown.
This breakdown made me become reclusive.

I moved back to my parents home and mostly stayed in. I spent my time reading religious books, and trying to meditate. I lead a simple life, while being vegetarian, non-smoker, abstaining from all sexual activities, non-drug or alcohol user. Simple diet. Apart from reading my self-help and religious philosophy books, I also went for peaceful walks in the countryside and on the beach. Solitary: My self and the universe. I distanced myself from my friends and lead a simple life. At the time, there was also a economic recession so no pressure to get work.

>>The experience<<
One day while laying on my bed (in the country), doing basic breathing relaxation/meditation, I had a profound experience.
I was extremely relaxed but still conscious, laying flat on my back with my hands at my sides and my eyes slightly open.
I experienced my being (soul, spirit, mind stream) leave my body at the top front of my head and spiral slowly out of my body into a dazzling pure white endless expanse of light.
As my being entered the white light, I experienced the real world of physical things fade or dissolve and be replaced by the white light.
The white light realm was as endless as the night sky but had no physical floor, so was simply everywhere and was very serene and dazzling.
At this point, I became fearful of the unknown as I realized I did not know what was happening. My being returned to my physical body in the physical world with a slight jolt, and I wiped my eyes and got up a little shaken and confused.
I did not share this experience with anyone at the time as I feared that they may think I had gone mad or was on strong drugs.
For a couple of weeks following the white light experience, I experienced a serene tranquil state, where the universe appeared to be perfect, with all its parts in perfect synchronicity with each other, almost as each part of the universe was part of a humungously massive symphony made by GOD, with parts fading in, playing their part and then fading into the background while other parts took their turn.
Every thing was perfect. Everything was in complete unity. Everything was at peace and I was completely absent of conflict, worry, anxiety, ambition and was perfectly content. Perhaps even perfect (without anyone knowing).
Sadly, this elated state did not sustain and my mental state eventually deteriorated.
Also, not having an understanding of what happened or direction of how to handle/control/master it, my circumstances also deteriorated.
I eventually re-intergrated back into normal life and hooked up with old friends.
I also started to get fairly bad anxiety which I have suffered from in different degrees of severity since.
I have also recently been diagnosed as having low testosterone, which can cause fatigue, chronic irritability, vulnerability to bouts of anger, low libido, and cognitive impairment.
Recently, after my brother dying, and after numerous other bad events, I have returned to searching for an explanation as to what had happened to me during these experiences.

>>>Early Life<<<

I was born in 1973, severely premature.
During my birth, I was read the last rights by a Catholic priest as I had stopped breathing and had no pulse for approximately a minute.
I was not expected to live for longer than a couple of weeks, or a few months max.
I spent 3 months at the hospital in an incubator with no physical contact from my parents (as this was the norm at the time).
Eventually I was allowed to go home with my folks, but had chronic eczema all over my body which continued for the first 7 years of my life.
During the first few years, I also suffered numerous respiratory problems and was frequently rushed to hospital after turning blue. I was diagnosed as having asthma at age 6.

My family life was generally good, with my parents being really kind and caring and very moral.
I was a very moral kid as I grew up, with very clear views of what is right and what is wrong, fair and honest.
Unfortunately, this honesty and fairness caused conflicts between myself and the other children of my age, as all of my friends seemed to be always up to something naughty. Either stealing, lying, bullying etc.  I got into trouble frequently as I used to tell them off and try and make them be nice.
Although my relationships were turbulent because of my moral, non-criminal stand point, my motivations were always for the right reasons; there was no malice in my heart.
I did often get bullied as I had eczema, asthma and was slightly obese.
At the age of 11, after watching Karate Kid at the movies, I and a couple of my friends decided to start karate at the local karate club.
Although I was overweight, and physically inferior to most kids of my age, I really took to karate.

Later in the same year that I started, all the kids from the new school I went to also started karate. Many arrogantly assumed they would wipe the floor with me, being superior to me in body and mind. However, my spirit was stronger than all of them and I beat all the kids that turned up, with each of them leaving one by one after taking a thrashing.
Through my secondary school years, I got more and more keen with karate, and after about 3 years of training, I had lost all the excess weight.
I also had become the top junior student at my club, with my head karate teacher moving me up to train with the adults at the age of 13, as non the kids my age were no longer competition for me.
At the age of 15, I won a local championship, in one category and the free fighting category was cancelled as the other kids in my belt/weight category did not want to fight me.
By this time I was training 7 days a week, sometimes 2 or 3 sessions a day, sometimes at more than one club. While all the other kids of my age went to the park to participate in illegal and loutish activities, I trained with single-minded focus.
During this period of intense training I also had one or two unusual experiences, while free fighting, at times, I found my body moving on its own in perfect synchronicity without any editing of my thoughts. With my limbs simply performing perfect strikes against my opponents leaving me as a passenger watching the display.

I continued to train.  At the age of 16, my older brother introduced me to pot, and although I did not smoke extensively, around this age I also started to go to the youth night clubs and took an interest in girls and booze. My training suffered. At 17 and a half, I met my first serious girlfriend and fell head over heals in love. This love lasted 6 months, but sadly for me, my girlfriend was coaxed into sleeping with someone else, who then split us up.

I think that I may have also had low testosterone at this time, as I was often tired, and apathetic. And this leads me to the period of the my retreat shortly prior to my religious / out of the body / near death experience.

Since then I have discovered that similar experiences have been documented by numerous people and can also be found in several religions. The one that most closely match my experiences that I have found can be found in Dzogchen/Bon, the ancient Tibetan religion that predates Buddhism.