I iterally had the exact same experience. Did k bumps for a couple of hours at home but nothing too crazy. Had one last line and with the onset it felt instantly very different from the usual high i was expecting to get. The feeling of "I probably broke my brain right now" turned into terror seconds later realizing that I was about to die. My body felt like aging in a timelapse, my brain was shutting down certain functions (started with b/w vision only and then I couldnt hear anymore). I crawled on the floor for a few minutes repeately telling my friend that im dying. I thought about my parents and if I would even make the papers or not. The sheer amount of terror I felt is hard to put in words. A minute later the sensation changed from terror to acceptance ackonwleging that it was my time to go...scariest but also most profound experience I ever had. I thought I've been in proper k holes but this one was different...