This thread is nowhere near as interesting as it could have been...
There is an acupuncture/pressure point mid way between your chin and lower lip (the ladiomental fold) that can block a gag reflex, try pressing there whilst on the surface. Some practice may help deprogram it, or make it easier to control.
Don't resurrect old threads to state the obvious. He knew what the gag reflex was.
Definitely don't doubt Dawn - not if you value your life
Good image though.
One thought - I have found some mouthpieces cause a horrible gag reflex for me too - for example the recent Apex ones which have a thing a bit like a horse bit and I find myself nearly vomiting with these. The older style mouthpiece on nearly all regulars I've never had an issue with