Weirdly enough, it might be. There are videos of people deliberately testing hypoxia. I've seen one where the person controlling the test told the participant "you know you are dying right now, right?" and the participant responded "Oh" with a big smile. Now maybe the participant was more chill because they knew beforehand that they weren't actually going to die. But they were still completely non-phased watching their brain shut down in real time.
I'm opposed to the death penalty. But if I had to choose my own way out of this world? Hypoxia is probably top of the list.