On larger ships it’s harder to get sea sick because the ships are so large you don’t feel much motion. However on some of the smaller Fantasy Class Carnival ships, you can feel a little motion. There are also variables that can enhance the motion or cause sea sickness. Rough seas is one of those variables as is alcohol.
If you want to feel less movement in your cabin then you should pick a cabin that’s lower (Riviera Deck) and as close to mid-ship as possible. The front of the ship and the higher you go, you are going to feel more motion.
First and foremost if you think you’re going to get sick, get something before you step foot on the ship. Not only is it much cheaper but it’s easier to be proactive than it is to be reactive to sea sickness. Once sea sickness hits you, it’s hard to make it go away until you step on land again.
You can get some medicine on-board from the medical center or guest services or even room service. I do have 6 different things I take with me just in case when I sail. These are all over the counter and can be purchased on Amazon.