Thanks for the input. Collapsing on any surface could inflict damage, and even on sand, there is the risk of landing face-down in the sand. The knee-pads and helmet are a good idea.
I am more scared of blacking out doing apnea walking than doing dynamic in the pool with a buddy. In the pool I am unlikely to get hurt, but on a hard surface there is the risk of impact between face and floor.
Once, when I was about 13, I was alone in a school playground, and I fell and landed on my back on the tarmac. It was not even a fall from a height, just from a standing position, but my head hit the ground with terrible force. I have no idea if I was knocked out, or for how long. I saw a flash of white light on a black background, and then found myself lying on the ground, in so much pain that I thought I had broken my back. I soon realised that I could move my legs, so it couldn't be that bad, and then I just about managed to get up and went back indoors, still in a lot of pain but pretending that nothing had happened. I didn't want to admit to having a stupid clumsy accident, and get laughed at.
That was not an apnea-related accident, but still it shows just how serious these things can be.
