A lot of people's feet swell because the ship moves...when the ship moves blood "leaves" your feet and goes mostly to your brain and your equilibrium area. People who get seasickness, suffer mostly because there is an imbalance of blood and pressure within their equilibrium area. What does this have to do with feet swelling? Well as blood rushes to your head and fuels your heart and equilibrium, your brain and heart then realizes a shortage of blood bellow your abdomen. When it sences and imbalance it may then send a surge of blood to your feet which in turn makes your feet swell and possibly irritable. This may go on for several days untill your brain reaches a constant ration of blood through out your body. Although im only 16, I learned this from my internship and the neurology department at Rockdal Hospital. Hope this answers the swollen feet and sea sickness question!