Swedish freediver Annelie Pompe explains how it feels to experience "freediver blackout":

A freedivers blackout looks much worse from the outside than it is experienced from the inside. In fact, it might be worse observing a blackout than having one. My last memory from the dive is only of having a good feeling of strength, swimming up towards the surface and next breath, having been to 131m depth I believed that I was on the way to break a world record. I spent what felt like an eternity underwater. And I obvioulsy spent a lot of oxygen swimming up with the monofin. My legs was obviously filled with lactic acid, but I could handle it. I remember seeing the safety freediver and being happy I was getting close to the surface. This is what’s scary with a blackout. It’s sudden and without warning. I suddenly started dreaming. The dream was just like a dream at night. Physiologically the hypoxia (lack of oxygen) had made my body shut down. As I ascended the lungs expanded and the pressure made the oxygen push back from the blood into the lungs, which makes the probabilty of a shallow water blackout occur near the surface. It’s also more likely to happen if you breathe to much and fast before a dive. What I knew, but was not aware of in my dream-state was the safety freedivers grabbing me and aiding my lifelss body up to the surface.

Next thing I knew I was transferred from the dreamworld to the reality. The sun was in my face. People were watching and talking reassuringly to me. It took a few seconds before I’d realised what happened. I breathed and felt a urge to cough. My chest rustled and I coughed some specks of blood from a lung squeeze. Someone gave me a regulator to breathe oxygen. There was silence around me, and I felt sad to have let the others down. I closed my eyes and focused on breathing. It’s all I could do for a few minutes. Dissapointment. And a decision to try again.

Photo credit: Annelie Pompe photographed by Nanna Kreutzmann.