CruiseStar
Less of a concern than most first-timers assume
Modern ships use stabilizer fins that dramatically cut down on rocking compared to older vessels, and most Caribbean, Mediterranean, and coastal itineraries stick to relatively calm water for the bulk of the trip. The real risk goes up on open-ocean crossings, certain Alaska routes through exposed passages, and sailings during hurricane or storm season, not the average weeklong port-hopping itinerary most first-timers book.
Cabin location is a real lever here
A cabin that's both midship and on a lower deck sits closest to the ship's center of gravity and pivot point, which meaningfully reduces how much motion you feel. Cabins at the very front or back of high decks feel every bit of a rough day, so if motion sensitivity worries you, that's worth weighing more heavily than the view.
What actually works if you do feel it
Over-the-counter options like meclizine (Bonine, Dramamine Less Drowsy) work well for mild to moderate symptoms, and prescription scopolamine patches are common for anyone with a known history of severe motion sickness. Acupressure wristbands help some people as a drug-free supplement, though the evidence there is more anecdotal than clinical. It's worth packing something even if you've never gotten seasick before, unfamiliar motion, a rough weather day, or a longer open-ocean stretch can catch people who've never had an issue previously, and it's a lot easier to bring medication than to track it down once you actually need it.
If it does hit you
Most people who feel off in the first day or two find it eases as the body adjusts, sailors sometimes call it finding your "sea legs." Staying on deck with a view of the horizon, keeping hydrated, and eating something light rather than skipping food entirely all help in the meantime, and the ship's medical center stocks basic remedies if you didn't pack any, though usually at a premium over what you'd pay at a pharmacy at home. Symptoms that don't improve after a couple of days are worth mentioning to the medical staff rather than toughing out.