For Lauren Hill, the moment John Martinez collapsed on the floor at Rise Up Fitness Center did not feel like heroism. It felt like instinct. Hill, a 31-year-old traveling CT and X-ray technologist from Spring Hill, Tennessee, had been in Craig only a few months when a routine evening workout on April 21 turned into a fight for a man’s life. About three minutes into class, Hill turned around after grabbing weights and saw Martinez on the ground. …