My dad used to regularly decompress navy pilots to 25000' and they would swear blind they never passed out...until they opened their shirts to find all the writing on their chests
Something I want to try one day, maybe when I visit the USA I can find somewhere. Not heard about anywhere in the UK that offers this service to private individuals.
But I agree, not everyone would pass out, people survive for days at > 25000, but these tend to be the fit, mountain climbing types, not pilots
By the way the 250000 ceiling is just an FAA number as this prevents having to have the high altitude endorsement to fly the aeroplane at any height. Likely the TC'd mooney could reach much higher.