Blackwood
Contributor
I have had things like this done to me numerous times by instructors, and I have found it only beneficial for me. In cave training, one of our first dives involved our masks and one of our regs being taken unexpectedly at the same time and we had to buddy breath on exit. It's stressful to be blind, trying to get air off a buddy who also cannot see anything and then have to buddy breathe in 52F water with no mask on. All the other stuff that has been pulled on me was not nearly as stressful as being without air.
There seems to be some people who are adverse to stress testing and I do not understand why. If you can't deal with stressful situations (and the thing that is likely to put someone under the most stress is not getting air) then should you really be doing technical diving? I am surprised anyone would be satisfied with training that would not stress them in this manner.
OOG shouldn't be a stressful situation. If it is, you (the proverbial you) aren't ready.
I don't particularly care if an instructor does or does not turn off the post I'm breathing, but I think it's potentially more instructive - so to speak - when he/she gets me to do it to myself.