Asked by: Paul Verrinder, Birmingham
Motion sickness in general is caused by a conflict between visual information and the organs of balance, and occurs to a greater or lesser degree in all the higher vertebrates. Some animals, including rats and horses, are unable to vomit but will feel the nausea and distress of seasickness nonetheless.
Antarctic explorer Ernest Shackleton took ponies with him and recorded in his diaries that they suffered terribly during stormy weather on the way there. Even fish in tanks can show signs of distress during rough sea crossings, though this is probably more to do with vibrations in the water than visual disorientation.