I was there when they pulled him out, we were doing our surface interval. Starflight came with a chopper along with a couple of ambulances. Not much they could do for him I guess. He was bleeding from the mouth and nose. They administered O2, and I heard he was in and out of consciousness. Sounds like he was at about 50' when he passed out and was taken to the surface(taking advanced open water, I believe). Medical help was there quickly and there were LOTS of first aid, O2 providers, etc. helping on the scene.
Along with everyone else there, I have speculated on the causes, but it's just that, speculation, so I won't post it here. In addition, I don't know all of this as fact, so please don't take it as such. We'll know more in a couple of days.