If you are seasick, the boat’s moving makes your body feel ill — your stomach turns, you may go pale, you may need to sit still. It is the sea cousin of feeling ill in a car or a plane. Some people feel it on a short ferry; some never do. Looking at the far line of the sea, or staying out in the air, often helps more than sitting inside. We say I get seasick (it happens to me) or I feel seasick (right now). It is an ordinary word, not a doctor’s word, and not a joke, though people do smile about it once they are back on land.