Ginger always seems to help calm the stomach. But the core cause of sea sickness is an imbalance between what the ears feel and the eyes see. If one starts to feel uneasy on a ship, the best remedy is to get outside and look for the horizon. Once your eyes sync up with the ears, the brain relaxes. Past that, there's the simple mind over matter. You know you are on a ship, you know it moves up and down in the water, so you're reminding your brain that what the ears feel is right. But its usually pretty easy to find a window or just get outside when you're sailing.
That's all the natural stuff. If you are concerned enough, you can get Dramamine from anywhere that sells OTC meds. You can also get a patch prescribed from your doctor that helps with it.
I've taken Dramamine maybe once in my life and that was at least 15 years ago. My first cruise, on the last night I know we were hauling it. I was in a forward cabin and noticed the up and down motion. But hey, I reminded myself I was on a cruise, and since it was dark, my eyes didn't see anything anyways, so I was fine.
If you are on the cruise and start to notice a problem, sometimes its as easy as closing your eyes for a moment so the brain isn't getting conflicting information and then just relax ... you're on vacation remember?
Disney Dream - Dec 2012 4n Bahamas
Carnival Imagination - Dec 2011 4n Western
Carnival Imagination - Nov 2010 4n Western
Costa Atlantica - Dec 2009 7n Eastern
My opinions are mine and mine alone. They do not represent the opinions of The Walt Disney Company nor any of its subsidiaries.