The same thing happened to me about 4 months ago except it was deadlifts. I think I somehow let my back rotate a bit when I was on my way down. An MRI revealed a slightly bulging/dehydrated L4/L5 disc. My leg days have since been infrequent and very light with no deadlifts at all. My chest is looking better than ever though...
The sad thing is I haven't been doing a powerlifting routine at all. I decided a couple of years ago when I started lifting that I'd rather look good than be able to lift super heavy weight. I was only deadlifting about 1.2 times my body weight.