Re chamber runs, many years ago I participated in a 25k rapid decompression session prior to a Mirage ride at ARDU. As discussed above ... but the alarming thing was that I didn't recognise any symptoms myself and duly nodded off into la la land.
We were tasked with the usual pencil and paper exercise (I still have the paper to remind me) and I was so sure at the time that I was doing real fine. Post O2 I was more than surprised to see the gibberish I had been writing.
Needless to say, in later airline flying, I was most attentive to O2 matters ... always.