Old-skool scuba certification used bare-bone instruments and ours took place in a deep/frigid quarry.
I had the sniffles the week before; so, I used some Afrin up my schnoz.
When, we dove-in for the final check-out, I got to about 10ft and my head felt as if in a vice.
By about 20ft down, I signaled the 'cut-throat' hand signal and he urged me to come down.
I did the opposite and went up to the surface!
I got the PADI cert. anyways that day because he said something about "I knew my limits" after he saw I was not letting blood.