The actor played Dr. Jack Shephard on the desert island show, which wrapped last year (10), and was required to film several scenes in the ocean.
However, one of the shoots went wrong after Fox - who admits he's a poor swimmer and terrified of water - spent an entire morning nursing a nasty hangover.
He tells Britain's The Graham Norton Show, "It was literally the part of the show I disliked the most, the water sequences. I'm not very comfortable in water and every time I was asked to do stunts like that it freaked me out. I didn't learn to swim until I was like 22.
"There was one water sequence I did early on in the show and we (the cast) had all been partying the night before... I was required to go pretty far out in the water and had to do a lot of really hard swimming and I spent the morning throwing up. It was a terrible morning."