I read an article many years ago by a father who was looking for a cure for the early season seasickness his kids experienced at the beginning of each sailing season. He and his wife didn't have that problem.
Then he wondered if the waterbed they slept in had anything to do with it. So at the end of the season he bought waterbeds for all the kids. When the next season came, none of the kids got sick.
I've had a waterbed for 40 years and the only time I've been seasick was one time when I was out too late, had too much to drink and went out early the next day in sloppy seas.