In the 2003 Academy-Award-nominated "Master and Commander: The Far Side of the World," intrepid sea captain Jack Aubrey sails from old-world Europe, around the southern tip of South America, and lands in the exotic Galapagos Islands. Despite encountering rough seas along the way, and an even rougher battle with a rival sea captain, "Lucky Jack" never once succumbs to motion sickness. And at the end of the film, we presume he returns to mother England with glory for his homeland.

In real life, most travelers aren't so lucky. Travel by sea, land or air and you'll usually find someone in the cabin getting sick — not from the galley grog or packaged peanuts — but from the movement.

"When a person moves, his eyes, inner ear, and limbs all sense the motion and send signals to the brain," says Dr. Michael Stewart, chair of otorhinolaryngology at Weill Cornell Medical College and otorhinolaryngologist-in-chief at NewYork-Presbyterian Hospital/Weill Cornell Medical Center. "The brain, in turn, then instructs the body how to respond to the movement."

When all parts of the body feel the same motion and the brain receives identical signals, the situation is fine. However, when traveling, this doesn't always happen. An airline passenger may see a static cabin while his limbs and inner ear sense the jostle of turbulence; the eyes of train or car passengers may see scenery rushing by, but their limbs and inner ears sense little movement. Situations like these result in mixed signals being sent to the brain, resulting in a rush of confusion and feelings of nausea, dizziness and fatigue — a.k.a., motion sickness.

"There are medications that can help," says Dr. Stewart. "Dramamine and antihistamines; or Antivert (Meclizine), which requires a prescription; or actually even valium, can reduce symptoms by deadening the senses and reducing input to the brain. But, they'll all make you drowsy." Simple non-drug measures such as looking at the horizon or closing your eyes may work with some people, too.

Some passengers — typically, ship travelers — succumb to a paradoxical kind of motion sickness known as "mal de debarquement." These passengers feel fine on the high seas, but get queasy and disoriented once back on dry land. "For reasons that physicians don't completely understand, these people calibrate easily to motion, but have difficulty calibrating back to not moving," says Dr. Stewart. Fortunately, "mal de debarquement" is rarely serious and typically fades away within a few hours or days. However, if necessary, it can be treated with the same medications as used for motion sickness.

By Dr. Stewart in Salzburg, Austria.