Be warned. Inert gas sounds very good, but there is a very strong SI kicking in and most abort. I tested it!
SI is always involved regardless of the chosen method as survival is one of the most basic human instincts.
For the sake of my curiosity I tested how long it takes to pass out breathing helium.
I used double sided tape to attach a 100 liter plastic bag to a wall and I filled it with 99%+ helium.
Then I tried to push all the air out of my lungs and carefully got my head in to the bag up to my shoulders.
I began to take deep breaths while counting seconds and in 3-5s hands, face and feet started to tingle.
At about 10 seconds tunnel vision and hearing white noise came on fast and I don't remember after this point how long it took to pass out.