I have read some things about a mix of gasses called Carbogen or Meduna's Mixture, which is 70% Oxygen and 30% CO2. It was used in the past in psychotherapy to see the way pacients react to strong psychedelic experiences and is said to have effects similar to strong psychedelics like LSD and mescaline. Theoretically, carbogen works the follwong way: When the body detects large amounts of CO2 in the lungs, it is usually a sign that the individual is choking or drowning, etc. Logically, if CO2 levels rise dramatically, O2 levels fall to a life-threatening level. So if the body detects large amounts of CO2 in the lungs, it will trigger panic reactions because it thinks there is no more oxygen. This way, the individual feels like dying, even if there is enough oxygen to keep him alive. This leads, theoretically, to NDEs (Near-Death Experiences), which are described to be like a very strong hallucinogenic trip. I never tried this, because I'm kinda afraid to do this. If anyone has experiences or more info on this, pls post.