I screwed up my back ~20 years ago. I never had it looked at, but I suspect it's one or more blown disks. Once or more a year it goes out, and the pain leaves me gasping for air. It lasts ~5 days before I'm more or less functional, with the first two or three being almost unbearable. It'll take me 15 minutes to even get out of bed, or roll myself over. My speed moving around once I get on my feet is glacial.
I've hurt myself almost as much several times with a hammer, but the pain is fleeting enough not to matter. My back just never stops when it goes.
Edit:
Oh, how I screwed it up was bullpinning wood into compacted road base. I used too much back, and not enough shoulder. After I did it, I was driving around with a heating pad plugged into an inverter for half a year, and my back hurt chronically for ~10 years afterward. That's mostly gone, but it was replaced by the excruciating pain mentioned above. Not sure which is worse :^/