There's not many medically documented cases period but there ARE cases on here of people who have survived after getting help and have said that they have been left with: 1) brain damage 2) heart damage 3) bladder issues.
I think it's false to act as if this is a 100% method as long as you don't call for help or get found...as long as your SN is fresh, etc. First, we don't know that because many people don't come back to report. This forum seems to discourage the ones that do... I've seen the people get raked over the coals by people saying they didn't follow protocol, or they failed because of this or that reason....or they are "pro-lifers" who were faking it, despite there being no evidence of that. Some of these folks DID follow the protocol exactly but after 40 minutes, were still not unconscious and had to make the decision to get help because they were concerned about permanent damage otherwise.
I'm not saying this as a "pro-lifer" as this is a method I am seriously considering... but I have done tons of research, searches, etc on here. I think people should be informed of the possibilities of what could happen, what to expect, etc.