There are many steps you can take BEFORE you get onto a ship to help you prevent seasickness. In many cases, seasickness is quite preventable.
First, make sure you eat VERY healthily the night before. Don't drink a lot of alcohol. Don't eat heavy, greasy foods. Drink a lot of water, eat light foods like salads and grilled chicken / fish. Get a lot of sleep. It can be exciting to go on a cruise, and you want to celebrate! But remember that your cruise can be a disaster if you're seasick. Take it easy until you get your sea legs.
On the other hand, don't let your stomach be completely empty - because then the acids that start to build will really bother you. Eat a light dinner the night before, and a light breakfast. Keep crackers, toast and apple slices with you. Nibble them during the morning.
When you get on the ship, when the boat starts into motion, stay up above decks and find somewhere very breezy and fresh airey to sit. Keep cool water on hand - sometimes having a cool washcloth on your forehead can help out. But don't lie down - stay sitting up at least.
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