This happened to me in OW class... wasn't completely focused last day of OW (other issues on my mind) anyway first dive of the day, instructor gives us a briefing (what we are going to do), basically two tasks. Fin pivot, inflating BC orally and mask removal and replace. No biggie right? Well we descend (25 feet), I'm first in line, gives me the OK sign, OK back, gives me the remove mask signal... what do I do? Remove mask, spit regulator... nice, looking for regulator with no mask on is real fun... needless to say instructor promptly grabs reg and me and shoves it back in my mouth. Than I'm so flustered I replace mask, suck water into my nose and try to clear, when I finally do clear I am hacking and gaging with all the water... took me a few to regain my composer. He goes on down the line, of course everyone else does it without issue. So he comes back to me and makes me do it again... this time no issues.... oh well at least I didn't panic!