James Michael Grimes is sharing his incredible story of survival after falling overboard on a Carnival Valor ship. The 28-year-old tells "Good Morning America" he does not remember the events leading up to falling off the ship. Grimes says the next thing he remembers is fighting for his life in the Gulf of Mexico. For nearly 20 hours, Grimes treaded water and battled sea creatures. Miraculously, the U.S. Coast Guard spotted Grimes and hoisted him to safety.