I guess I should ignore everything I learned in the chamber.
So when we went to a chamber and slowly altitude increased while doing task, each person learns about their own body when they were deprived of oxygen. My reaction was typical....skin became very hot/redish and tingly. This training helped me while doing gliding (second solo) and not noticing that oxygen system stopped working...around 17,000ft. After noticing symptoms, I descended quickly and did light troubleshooting of an oxygen system. So yeah, you are dead wrong. There are plenty of notifications. Unfortunately, only military pilots go though training it seems.