What is seasickness?

Seasickness, like other forms of motion sickness, is thought to occur when there's a conflict between what your eyes, inner ears (which help with your balance) or sensory nerves sense. Often on a cruise you may not be able to see with your eyes that the boat is rocking, however your ears are more susceptible to sensing it. This results in mixed signals being sent to your brain which can result in nausea and vomiting.