A tractor-trailer slammed into a Dunkin Donuts shop in Chelsea this afternoon, after the driver apparently had a medical emergency, authorities said.The truck driver, identified only as a 48-year-old New Hampshire man, “lost control of his truck, struck a parked car occupied by two passengers, and careened into the building,” Chelsea Deputy Fire Chief John Quatieri told the Herald.Witnesses told police that the driver “got out of the truck and immediately dropped to the ground,” Quatieri said.