An employee was attending training and started feeling queasy/lightheaded during the module on blood-borne pathogens. He left the room and sat in the northeast stairway. A short time later, he fell down the stairs and was found unconscious on the landing below by a coworker. His coworker woke him up and asked if he was okay. The injured employee stated that he was okay, just tired. He was later hospitalized for a skull fracture and concussion.