EMPLOYEE MADE KNOWN OVER THE TWO-WAY RADIO THAT HE WAS GOING TO STEP OUT OF THE CAB OF HIS ROCK TRUCK TO URINATE. HE WAS FOUND MOMENTS LATER SITTING ON THE GROUND COMPLAINING OF BREATHING PROB LEMS. DURING THE PATIENT ASSESSMENT HE SAID HE HD STUMBLED AND FELL OFF THE FRONT OF THE ROCK TRUCK.