I am always concerned about getting headaches and nausea whenever I get out on the water. I don't get sick most of the time, but I know there is always a chance. When the water is calm, I am fine for the most part, but when the waves get choppy, I spend most of my time trying to keep my lunch down.
The worst dizziness I ever felt was on a whale watch boat. It was the end of the whale watching season and a storm was moving in. I was fine as long as the boat was moving steadily ahead with the motor powering us through the water.
When we stopped to watch the whales and the waves were bouncing us all over the place, I couldn't move because when I moved my head the smallest amount, I felt like I was going to throw up. And I knew I couldn't make it all the way to the bathroom at the back of the boat.
Also, it didn't help when a couple other passengers got sick right where they were sitting. That was by far my worst experience on a boat or ship.