I had just sent a route that was a pretty big tick for me and it was very early in the season so my headgame wasn't quite where it normally is. I topped out, celebrated for a short while, and then because nobody wanted to second it I set up an ab from a stake to retrieve the gear. The adrenaline had subsided by this point. I found the marked midpoint of my rope (recently shortened by removing 1.5m from one end), rigged an anchor creating two redundant lines from the stake at the midpoint of the rope, and because I was descending into a river I flaked both ends of the rope into a ropebag which I suspended from my belay loop. I forgot to tie knots in the ends of the rope. I descended using my ATC and a prusik knot attached to my belay loop. Everything was fine until one end of the rope zipped through my device. Fortunately my reaction was to immediately remove my hand from the prusik and it jammed with a very short tail left on my side. I was freaking out a little bit at this point and holding on very tightly to the rope. I was probably about 5 metres above the boulder strewn river. Once I'd calmed down a bit I made an anchor using some of the nuts I'd retrieved, reset my ATC and prusik loop, and did the slow prusik shuffle back to the top. I was saved life changing injuries or maybe death by my use of the prusik. Maybe the unequal rope lengths helped but I think the prusik would have jammed even if both ends had gone through the device. I used to attach my prusik to small loops on the legs of my harness until a friend pointed out that they weren't rated for much and it would be safer to use the belay loop. This also means my prusik knot is above my ATC. I am very glad of that advice now because if it had been below my device I might not be writing this.