Motion sickness (3.5e Flaw)
From D&D Wiki
You have a hard time getting around, on anything else but your feet
Effect: Any time you move more than 15 feet, you become sickened until the end of the round. This effect is constantly in effect when riding on an animal or vehicle until dismounting.
Roleplaying Ideas: You will most likely try avoiding any form of transportation, that doesn't involve you using your feet. You are also weary of dungeon features (or traps) involving conveyor belts, teeter-totters, rotating rooms and the like.