Whatever it's called (Suspension Trauma was the term back in 2006), it astonished me how quickly it could happen. I was at the top of the Bar Pot entrance pitch, assisting a novice, who had done all the club's usual training, up through the tight pitch-head. She was tired after a trip to the Main Chamber but I remember thinking we were 'home and dry' at this point. She struggled in the narrow section to get high enough to get off the rope. After what must have been only 5-10 minutes of struggling, with me providing the usual assistance from arms reach away, she started saying she was tired, and moments later, she was fully unconscious on the rope.
From first encountering issues that limited her movement, to becoming unconscious was probably around 15 minutes.
Thankfully I had the rope from the main pitch, and the guy below me had enough knowledge of how to do a cut rope rescue (and first aid training for once she was down there) to talk me through it from below, and the outcome was good.
At the time, I was under the belief that she had gone unconscious due to suspension trauma. Is this incorrect? Or is this just incorrect terminology these days? Either way, it was alarming how quickly a tired and stationary caver in a harness can succumb to this and I have always been surprised that it has never been a bigger issue in caving. Anyway, it can only be a good thing for BCA to be making cavers aware.
Interestingly, I believe the advice in 2006, when the above incident happened, was to position the casualty with their core body and head above their legs to prevent the potential sudden rush of poisoned, CO2-rich blood from the legs to the brain. This is what was done in our situation, but interesting to see that the advice has been updated to go against this previous advice.