I think I may have told my story before, but I had a decompression as well. Old ECS plumbing in my aircraft often makes for some bleed/ECS related adventures. Such was the case when, after putting my ECS into manual mode due to another somewhat unrelated caution, I started getting some minor pressure cycling. Eventually brought the throttles back to idle to slow down while at 35k ft, and all of a sudden my cabin pressure dumped instantly from 12kish (normal schedule) to ambient/35k. Thought my brain was going to pop out of my head. Quickly switched back to auto ECS, and noticed that I had symptoms of hypoxia or something. Let my flight lead (and notably, I was the brand new FNG at the time) know sheepishly, and we started an emergency descent. At no point in that process did I activate emergency O2, in spite of it being bold face. Chalk it up to hypoxia related mental confusion or whatever else, but bottom line, I didn't follow the two procedures that will save your life. #1, get down immediately. I waited way too long to communicate, bring my lead into the cockpit with me, and then follow him. He should have looked out and suddenly seen no wingman because I was already bullseye nose low getting into breathable air. #2, emergency O2. No delay. Don't second guess it.....use the bottle before it is too late to use. That little omission has killed dozens of better aviators than myself. Those two responses need to be instantaneous and without question, even if in the back of your mind, you are questioning whether or not you are really hypoxic/suffering from DCS/whatever other physiological issue. Some of these considerations are peculiar to the type of flying I do, but the big boldface #1 and #2 are not. Don't ask ATC for permission, don't try and tough it out, don't think that half a boldface checklist is good enough, and don't start troubleshooting an obviously broken system before you are physiologically safe from its effects. Just my take, lucky to actually be writing this.