Oh my poor back!

How did I injure my back while brushing my teeth? Well, it really has little to do with brushing teeth. Actually, when I was a teenager, I had hurt my back a few times pretty seriously. Since then, my back has had lingering problems. So the other day, early in the morning when I was brushing my teeth, I bent over the sink to spit out the toothpaste when my back just sort of clicked and gave out. It just happens randomly on occasion, and there's nothing I can do about it. I just have to stop, try not to move, and rest. Oh my poor back!