An off-duty firefighter who sprang into action during last fall's massacre at the Route 91 Harvest festival in Las Vegas -- where a gunman killed 58 people and injured hundreds -- spoke about his harrowing experience yesterday to a room full of Massachusetts firefighters and urged those struggling after bouts of trauma to get professional help. Jesse Gomez, 45, a 15-year veteran with the Clark County Fire Department that encompasses Las Vegas and has jurisdiction over Las Vegas Boulevard, was at the country music concert Oct. 1, 2017, when Stephen Paddock began shooting from the 32nd floor of the Mandalay Bay Resort and Casino.