[Marwan]

hmmm maybe the vic is ill with something or got vertigo at some depth..when i read the first post i can imagine one scenario leading to that...if the diver is not too comfortable with the water and for some reason inhales water through the reg or gets water in the mask...they can panic and instead of attempting to clear the regulator they head for the surface in panic (tunnel vision, get me the hell outta here)..depending on the depth they might not make it conscious, which would explain both the water foaming and the unconciousness..but that doesnt tie in with the DM's account of the victim falling 20 feet ...that could be caused by a medical condition perhaps...
sounds like it was managed well though..