When you feel like you might throw up, that's nausea. I know you're feeling sea sick, but if our boat sinks, nausea will be the least of your problems.
Nausea gets its root from the Greek word for ship, naus, so it might have originally meant sea sickness in particular. Remembering this origin might help you spell nausea correctly too, since it ends with “sea.” But nausea can strike on dry land just as well, from eating the wrong thing, catching the flu, reading on a moving bus . . . just thinking of it all makes me sick to my stomach.