One of my scariest moments as a Divemaster I was with an Advanced Group at the 85’ platform and one student bolted to the surface... mask off reg out. I noticeds one of our DM candidates already had ahold of him so I was staying back some 10-15 feet to let the guy handled it and then the student kicked and punched his was out of the DM candidates grasp (this was around 60 feet) and still reg-less and mask less fled frantically to the surface... I surfaced shortly with a baro trauma... after he sky rocketed and asked him what was up. He told me that his regulator had quit working. NOT. I checked it and it was breathing just fine... he panicked and refused to accept that.. so we got him out of the water and on O2. He’s lucky he didn’t have an embolism.