NCIS Season 3 Episode 23

Gibbs is injured in a bomb blast on a Turkish merchant ship, which puts him in a coma. He wakes, suffering from an unusual form of amnesia, where he thinks it's 1991, when he had been in a coma from another trauma, having no memory of the last fifteen years... including his team. The physical trauma to his brain does not explain his amnesia, so the team tries to uncover the possible psychological reason for his amnesia, while also trying to determine who, and why the bomb was aboard the merchant ship in the first place.