When one enters that stage of yoga, if they've been a good little yogi and done the preliminary physical preparations (which may take decades (or you hit the jackpot and are born into a magnificent constitution, maybe a few years)), they can begin the real 'yoga', which is mainly just seated meditation. It is akin to performing surgery on the central nervous system and most importantly, its main channel running along the spinal column(shushumna).
If one is not prepared correctly, as an inexperienced surgon performing brain surgery, cutting the wrong cords or becoming stressed/frightened at the wrong time could be disasterous when operating on your subconscious autonomic nervous sytem (and even deeper!) there is a reason everyday humans cant control that stuff voluntarily!
joint damage etc pale in comparison to cutting the wrong wires on that low level state in the nervous system. Think voluntarily giving yourself psychosis or Multiple Sclerosis or launching a schizophrenic rogue subroutine in your body that randomly regulates temperature, making you icy cold one moment, pulling blankets over you, then burning hot 3 minutes later, as you run for the cool bathroom tile floor in the basement to lie down on.
But hey, what else are you going to do in life?
But in general, symptoms can include some/all of the following, and vary in severity depending on how slowly you progress, how clean your lifestyle, etc:
* Energy surges - intense feelings of heat/electrical sensations in the body, typically in the spine (I've been woken in the past with electrical sensations surging through my body) * Dietary issues - one of the nerve passes near the stomach and apparently can alter appetite as well as making you intolerant to some foods (I read of one guy not being able to keep water down for several days), etc. * Sexual side effects - feeling intensely horny or totally disinterested * Insomnia * Headaches, feelings of congestion * Hallucinations - auditory, visual, kinesthetic * Spontaneous out of body experiences
Apparently these all settle down over time but can be a bit unsettling (e.g being woken in the night to ghoulish laughter, but there's nobody there).
On the plus side:
* Feelings of intense bliss/ecstasy, contentment * Mental clarity
I've only experienced a few of the above negative side effects, and generally only mildly. But the Supreme Fire exercise has kicked things up a gear. Plus, I'm almost able to perform "full khechari" (look it up). My body just wants to do it. Spontaneous yoga can happen sometimes. Your body knows what it wants given half a chance :-)
As for joint damage - yes that is a definite risk. Never force the lotus position since it can put pressure laterally on your knees which can damage them over time. Also, there's debate around inversions (who'd have thought putting your entire body weight through your cervical vertebrae could be damaging :-D?), so while some people say they're amazing, I avoid them.
As it turns out, one of the most useful sitting postures places direct pressure on the perineum. This is traditionally done with the heel (siddhasana) but can be done with a prosthetic. Roll a sock up and sit on that. I use that on a Zen-style meditation bench to spare my knees sometimes. So you don't need great flexibility, certainly not to the level of the hyper-flexible people in yoga magazines.
A lot of it is common sense - don't force yourself with either the physical postures, or breath retention, and listen to your body. You need to activate the parasympathetic nervous system and operate in that mode. The other thing to bear in mind is you can have a delayed reaction. So you might do some breath retention, and feel great. So you do more. And more. Then that night you get the congestion/headaches/insomnia. So just build up gradually over several weeks, and back off if you need to. It's no different to pacing yourself with weights at the gym.
The AYP site has a very helpful forum with people far further down the road than I am. If you're interested you'll find lots of information on that forum to peruse at your leisure, and a friendly community to answer questions.
I'm "into" mindfulness stuff as a mental exercise but now I'm feeling intrigued about experimenting with the breathing stuff (and generally the more physical aspects of Yoga) more. So thanks for the background and reading suggestions.
Yeah I think hallucinogens activate the same areas of the brain. The only 2 times I've ever felt totally, 100% contented was while tripping on shrooms and through meditation.
I went on a Zen retreat and asked the leader about whether they do energy stuff in Zen, and he just said "It happens on its own". I think all roads lead to Rome all traditions are basically teaching the same core practices. I think optimal results come from doing the breathing practices before mindfulness meditation. In fact, that's exactly what Patanjali wrote in his famous yoga sutras:
Physical postures (asanas) -> breathing (pranayama) -> introversion to progressively deeper degrees.
And once you understand the bigger picture, all the restrictions placed on monks make sense: conservation of semen for guys has a big impact (so either celibacy or tantric sexual practices), minimal diet (difficult to compress the abdomen if it's full of waste), waking early (there seems to be a connection with the circadian rhythm), silence seems to help, etc. Either way, there's plenty to experiment with. Good luck :-)