@furgar This happened to me. Had my wallet in my back pocket, not knowing it was causing imbalances. I only noticed the imbalances once it started to hurt like hell when I was doing heavy deadlifts. The physical therapist asked me if I put my wallet in my back pocket, and sure enough, that was the ticket. Caused my sciatic nerve to be pinched, which hurt more than it actually caused real damage.

Now I can lift even heavier without those problems, though try to stretch more often beforehand.