I don't have all the details because I didn't ask.
There was a diver that on the first dive that went down and almost instantly came back up. I had just retrieved my camera and attached it to my rig when the diver came up right next to me. He didn't signal OK, really didn't respond to the crew, started switching to his snorkel but switched back to the reg when the crew told him to. At this point I asked if he was ok, he shook his head no, and I helped tow/guide him back to the swim step. I then proceeded to the anchor line and waited for my buddy. Since the crew let more divers into the water and let us proceed with our dive I didn't give it much thought.
During the SI we found out that he thought he went to 50 feet but when Captain Mark checked the computer he had gone to 112. Not sure what caused him to come back up.
He laid down in the cabin until we started transit towards dive 3 at which time he came back out onto the deck. Since a bunch of us had gotten sick (myself included, but I felt better after
) I just figured he was just a bit sick. Surprisingly he geared up for dive 3 and was one of the first in the water. My brother and I took our time gearing up as I was one of the last out on dive 2 so was trying to get at least a 1 hour SI. As he approached the gate I saw the diver being towed in on his back, kinda stretched out, without his BCD. We waited until we got an ok from the crew before jumping in and then helped them retrieve the BCD (it was floating on the surface).
When we got back the diver was sitting up in the cabin on oxygen but seemed responsive. As soon as the last diver was onboard they pulled anchor and headed in (we were already at the cove). When we got close a lifeguard came out on a board, the crew told us to make a path, and the diver walked out to the swim step and got on the board.
So not sure exactly what happened.