One of the big drawbacks of cruising is seasickness. Luckily, cruise lines know this, and they'll go out of their way to help passengers suffering from seasickness. In most cases, you can simply talk to whoever is at the service desk and pick up some meclizine, which is a seasickness medicine. You can also ask for some ginger, which has been shown to help people cope with the effects of seasickness.
In many studies, ginger has actually outperformed typical medication used for seasickness, so it might be worth giving that a try first, especially if you're looking for a more natural solution.