Nicholas Mevoli of Brooklyn was taking part in the annual event, hosted by Vertical Blue, with 56 divers from 21 countries Sunday when the incident occurred, CNN reported Monday.
Mevoli was trying to reach a depth of 236 feet at Dean's Blue Hole in the Bahamas, the world's deepest blue hole in seawater.
When he surfaced, he flashed event-goers an OK sign, then 30 seconds later lost consciousness, event organizers said. Vertical Blue officials said they were trying to figure out what went wrong.
"Competition free diving has an enviable safety record but the sport can never be risk-free, something understood by all free divers," the organization said in a statement.