This is also from the famous blue hole in Dahab (Egypt). You can dive my trainingspartner Anton doing a warmup dive with his monofin just going down to about 15 metres. He stays there for a few seconds and swims up again.
We also had yoga lessons while staying in Dahab for freediving training. Our teacher Jana said: "The trick of balance is...concentration" - see us struggle with that
On 30th of June 2006, Olivier Haug attempted to break his own record in the discipline constant weight without fins (lake) in Hemmoor. He went down to 40 metres (previous 35 metres) - but had a blackout at the surface. So the attempt failed unfortunately.