We had a case recently here where a very experienced deep air diver was swimming around a dive site at around 180 feet and had a blackout underwater (still breathing, still swimming, reg in mouth, but not able to process anything) and sucked his tanks nearly all the way down at depth. When he 'came to' he made a direct ascent to the surface, but the low backgas made his whole rig too light and while he managed to do some decompression stops on his deco mix, he blew off most of his deco. He's alive, but still recovering from some of the effects (some blindness may be permanent).
CO2 buildup makes a huge difference in the narcotic effects day-to-day, so this kind of incident is more likely with both increasing depth and increasing workload.
At 100 feet I'd be a little bit surprised, at 150' I'd find this plausible when combined with high workload (squirming through a restriction sounds like plausibly high enough workload to me, but I've never been to this cave, so can't say...).
