I fell backwards down a flight of thirteen stairs without touching a single step,landing flat on my back with my left arm somewhat behind me,knocking myself out when the back of my head bounced off the floor (my wife witnessed all of this). Anyhow, I think landing on that arm severally bruised or broke two or three ribs in the middle of that set of left sided. I am in unbelievable pain,can barely breathe,and I ve had broken ribs in the past!