As you can see from the earlier posts, there are a ton of solutions both medical and natural.
If that fails, take 6 shots of tequila and forget about everything.
Although this sounds like a joke, if you drink alcohol, consider this option as well.
Many who get seasick do so because of the feeling of the ship's swaying or rocking. Alcohol tends to calm the nerves and affects the cerebellum causing varying degrees of imbalance, depending on the amount of alcohol consumed. Psychologically speaking, your body would be tricked into thinking the rocking or swaying is due to the alcohol buzz instead of the ship and you would not feel seasick. Instead you'd feel the pleasant buzz and really enjoy yourself.
Incidentally, when I sailed the Carnival Ecstasy one in the past, every crew member who gave us an introductory tour finished with "Thank you everybody...enjoy your cruise...enjoy your booze."