Well, in terms of what happened: in cave-diving the "line" is life. I was in new territory to laying my own line. It parted company from my reel, and pinged back under tension into the zero-viz murk behind me. I was in similar territory to that in my avatar... low, tight, constricted. As I stopped, the viz disappeared around me. In total I spent 50 minutes "off the line", the majority spent desperately trying to find my way home in complete brown-out. The last twenty minutes were the acceptance. However, I was too embaressed to think that I would criticised for not trying, so thought I better go out with a struggle.
That struggle got me out... I was using a second reel of line as a search line. This line was 3.5mm and the original line was 4mm. As I searched, the search line spilled and paid out into the cave, so I kept finding the "wrong" line. That was traumatic for the first few times. Finally, I found a piece of line which I was about to discard again as my own search line, when rolling it between my gloved fingers, realised that it was thicker... it was my line. "Oh, I'm going to live" was my simple thought.
It wasn't the end though. By now I was so wrapped and cocooned in my search line that I could hardly move. I took out my knife to cut myself free... the next I remember I am on my way with 300m of passage to negotiate before getting out.
A month later I was back to tidy up the mess I had left. As I collected all of the search line into which I had become entwined, I discovered that it hadn't suffered one cut...
Life-changing: I accepted my death as reasonable as I had had one hell of a life up until that point... I figured I had done more before 30 than most could even dream about in a lifetime. I was immortal for a couple of weeks afterwards. Now I have no fear of death, as everything I have is bonus. I do have to remind myself just how selfish this attitude is, wrt my family.