I sent a message leo  he has not read it or responded in in two days so I am bringing  this to the community's attention Well I tried this twice for 20 minuets. I tested  spO2 level with my s7 smart phone and it was below 95 percent that is not good.  My levels never go below 95 as I test them every day as part of my daily routine. Also the symptoms of numbness and pins and nettles  in the extremity's as well as in the head are signs of hypoxica  or lack of o2 getting to the brain. If you commit to this practice you could be doing permanent brain damage every time. As I believe the effects  are from lack of oxygen from my experience and test as well as my limited research.   Further more O2 SATURATION DOES NOT GO ABOVE 100%.   And leo's premise that you are getting  more oxygen is I believe is incorrect.  If you do your research you can see this for yourself.  I am all for breakthrough techniques but Not at the expense of the health or damage to your physical brain.  Please before you commit to this practice learn what it is doing to your brain and the mechanisms that are causing the effect. Let me be clear this is not a direct attack on leo I believe he is in error and I welcome him to do his own research into what I am saying just as I am asking you  for your own safety. Below is a extract from an  article by Joe miller if what he says is true you should do more research and test you 02/spo2  saturation yourself  then make a informed choice based on all your findings as to whether (Holtropic/aka  leo's "shamanic breathing) is right for you.   "You might think the problem is too much oxygen. But in healthy people arterial blood leaving the lungs is already nearly fully saturated with oxygen, even during quiet breathing. In other words, you can’t take in too much oxygen. Rather, the problem with hyperventilation comes from blowing off too much carbon dioxide. In normal breathing, small amounts of incoming air are mixed with a much larger volume of air remaining within the alveoli (the air sacs in the lungs where gas exchange with the blood takes place). This has the effect of maintaining an internal atmosphere within the lungs that contains a much higher percentage of CO2 than does the air outside (carbon dioxide makes up only a very small percentage of atmospheric air). CO2 levels in the bloodstream closely reflect the composition of this internal atmosphere, so that during hyperventilation, as more carbon dioxide is expelled from the alveoli, CO2 levels in the blood also fall. We tend to see CO2 as a waste product, something to be disposed of. But in fact we need to keep  CO2 in the blood within a certain range, because it plays an important role in maintaining blood pH. As CO2 levels drop during hyperventilation, the result is a higher, or more alkaline, pH. Because of this rise in blood pH, hyperventilation has an effect that might at first seem paradoxical—by over breathing, we actually reduce the amount of oxygen getting to the brain, a situation termed cerebral hypoxia. This became an issue during World War II. Hyperventilating military pilots tended to become confused and disoriented. Researchers studying conscientious objectors in the laboratory were able to confirm that hyperventilation led to a reduction in blood flow to the brain, which had long been suspected. Their supposition was this was due to constriction of cerebral blood vessels. This has subsequently been shown to be the case, and although the exact mechanism is still debated, it’s clear that a rise in blood pH  triggers arterial constriction. What’s worse is that when blood becomes more alkaline, hemoglobin (the molecule that transports oxygen in the red blood cells) tends to hold on more tightly to oxygen. This makes sense in the context of allocating oxygen to the tissues that need it most: metabolically active tissues that have consumed a lot of oxygen and need to replenish it will have also produced a lot of CO2. This creates a more acidic local environment, which in turn causes hemoglobin to release more oxygen. The reverse is true when conditions are more alkaline; tissues don’t get as much oxygen, because hemoglobin hangs on to it. Thus, the brain gets hit with a double whammy during hyperventilation—less blood flow, plus less oxygen being released from the blood."   I have been away from the Forums  as my path has changed dramatically and does not leave much time for this forum.    I still drop by from time to time and I hope you are all well , I  wish nothing but the best for you all of you.  Which is why I have written this post.  Now that I have brought awareness to this practice and its possible dangers I leave the rest up to you.  Do your research and stay safe.  I am not going back to my cave to do my work please do not expect me to respond as my withdraw from this forum is deliberate so I have more time to do what needs to be done on my path.  After I come to my conclusions in my work if any of it translates to things I may share with others,  I will but I am no where near that yet.  My new journey is just beginning. Hallucinogens have nothing to do with it.  Farewell and stay safe