May 24

Freediving Blackout- What’s It Really Like?

I reached the surface from my 83m/272-foot freedive and vaguely remember hearing the judge shout, “Grab her!” before everything went blank.

I was only out for about a second before I came back around, finished my surface protocol, told the judge “I’m okay,” then realized Robert, my safety diver, had ahold of my arm. “Ohh…I blacked out didn’t I?” I asked. The looks of you’ll-get-it-next-time and sympathetic pats on the back confirmed my worry.

Memory Loss/Confusion

The crazy thing about blackouts is that you don’t always know they happened until someone tells you. I often tell students in class that it’s hard to definitively tell a blackout is coming on, but that’s not the whole story.

The nature of a blackout is to shut down your conscious brain, thereby conserving oxygen for your more important bodily functions, like keeping your heart beating. A freediver awakening from a blackout will experience a number of things including disorientation, remembering strange dreams or simply a confusing time jump from the point of blackout to the return of consciousness.


It’s somewhat common after a blackout to experience a carbon dioxide-induced headache, particularly if the blackout occurred under a heavy workload. Following my 83m dive Dr. John Shedd, our on-site physician, brought me to the boat and put me on oxygen, which is always beneficial following a blackout. I experienced a migraine-like headache and just sat on the boat covering my eyes from the sunlight while the oxygen helped off-gas the CO2 from my system. Within about 10 minutes the headache subsided, but not without getting in a few punches first.


Extreme hypoxia puts a diver’s body under a high level of stress as it tries to maintain oxygen levels in critical areas of the body. Following a blackout its very common to feel extremely physically exhausted. The best thing to do is to give into it and sleep the whole mess off. After a good eight-hour night you’ll feel much better, though depending on the severity of the blackout you may find that it takes a couple of days to feel 100% again. Definitely don’t try to dive again after a blackout until you’ve had at least a day’s rest as it’s very likely you’ll blackout again.

Brain Damage?

Nope! Blacking out should not cause brain damage (ahem, unless it’s caused by something other than hypoxia!). A freediver undergoing hypoxia will blackout with a reasonable amount of oxygen in their system. Brain damage only occurs four to six minutes after the diver has reached anoxia, or a complete lack of oxygen in the system, which would happen several minutes following a blackout. With proper safety a diver should return to consciousness within seconds after a blackout. ***

So while blackouts are different for everyone, these are the most common reactions to extreme hypoxia that I’ve seen. If you’ve experienced or seen other reactions please feel free to add them in the comments section!

The important thing to remember though, is that all of these blackouts have occurred with proper safety. Blackouts don’t have to necessarily be traumatic events, but without safety there’s only one, pretty permanent result of blackout.

***I changed this section from “Blackouts do not cause brain damage” to “Blackouts SHOULD NOT cause brain damage” as research is still advancing in the sport and though much of what I’ve found (through outside research) over the years indicates to me that blackouts wouldn’t cause brain damage I realize now after some re-evaluation that saying they definitively don’t is too strong a statement.


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  1. Vincent


    As a freediving monitor for several years now, I’m very surprised by your brain damage assertion “Blacking out does not cause brain damage”. I would be very happy if you could send me any scientific or medical report that concludes to the same positioning. As far as I know there is no study actually, based on a reasonable number of person proving that black out has no impact on the brain…. Most of the time, freediver are young with a important brain plasticity which may hid any minor brain damage.
    Result is that freedivers are very often using the black-out as a indicator of their limit during training and such assertion is just confirming their approach.
    As a monitor I’m training freedivers and insist on the danger of the black-out. This is a preventive speach. Nobody knows how freedivers having black-out will be in 10 years…

    Your comments are more than welcome

    1. admin

      Hi Vincent,
      Thank you for your comments! For full information on the research that supports my writing I’ll refer you to Kirk Krack, head of Performance Freediving International. That agency has conducted a good deal of research into many different areas of freediving alongside organizations like the Diver’s Alert Network and Duke University. It is this research on which I’m basing my writing/teaching. You can reach him at kirk.krack@performancefreediving.com

      The rationale behind my statement that “blackouts don’t cause brain damage” revolves around the fact that a diver loses consciousness well before becoming anoxic, or reaching a complete lack of oxygen. As long as the diver recovers prior to becoming anoxic, there should be no brain damage. The real imminent threat of brain damage occurs 4-6 minutes after hitting anoxia, which occurs a little while after blackout if the diver does not resume breathing.

      That being said, research into freediving is far from 100% complete and I base my suppositions on the studies that I’ve read and been involved with, but I welcome any research to the contrary as this is a sport in which we are all always learning. Please feel free to send any such research my way!

  2. Vincent

    Hi ??,
    Thanks for your answer and the pointer to the research site. I will contact them.
    I did not conduct a deep state of the art research in the domain but contacted a searcher in the south of France (University non profit organization) working in this area and freediving doctors having being involved in the rescue of hunters. They are less optimist than what I read in your initial post and so, as I freediving teacher I prefer to have a preservative speech.
    I will contact the person you pointed

    1. admin

      No problem! I think erring on the side of caution is definitely okay as long as you continue to teach all the safety associated with blackout recovery/rescue, etc. What certification agency do you teach for?

      Good luck with your research!

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