The BBC recently printed a story describing a rare condition called mal de debarquement which causes dizziness, typically after a boat cruise, though can occur with airplane flights and even a long drive in a car with switchbacks (going up/down a mountain).
Two signs that a patient has mal de debarquement are if they feel a rocking sensation for weeks or months starting AFTER a cruise and two, if they're much better when in motion like vigorous exercise, but feel much worse when staying still.
Read the story here.
Unfortunately, no great treatment for this condition beyond displacement type exercises (walking, running, bicycling... but NOT on a treadmill or stationary bike).
This condition was also in an article by the Washington Post in 2010.
