This sounds like fun to play with: a blend of Co2 and O2... with higher than ambient CO2 levels. Unless your a COPD'er or freediver, the drive to breathe is via monitoring of CO2. Despite being more than adequately oxygenated, the high CO2 provides an impulse to breathe rapidly, elevated HR, sympathetic whatnot. Then.... apparently you have a psychodelic experience. Freediving results in some profound calmness. I wonder if it's similar? CO2 tanks and O2 tank are easy to come by. If you want to mix carbogen into a med type gas cylinder you'd need a transfiller though.