Motion sickness, also called seasickness, carsickness, airsickness or space sickness, depending on what one has been traveling in, is a condition in which the endolymph (the fluid found in the semicircular canals of the inner ears) becomes 'stirred up', causing confusion between the difference between apparent perceived movement (none or very little), and actual movement. It can result from lying in the berth of a rolling boat without being able to see the outside. Nausea is the most common symptom of motion sickness; in fact, nausea in Greek means seasickness (naus=ship). If the motion causing nausea is not resolved, the sufferer will frequently vomit within 20 minutes. Unlike ordinary sickness, vomiting in motion sickness tends not to relieve the nausea.

One particularly distressing thing about seasickness on a passenger boat is that the bathrooms tend to fill up quickly during rough seas so many seasick passengers have to vomit in public.

Sudden jerky movements tend to be worse for provoking motion sickness than slower smooth ones, because they disrupt the fluid balance more. A 'corkscrewing' boat will upset more people than one that is gliding smoothly across the oncoming waves, and cars driving rapidly around winding roads or up and down a series of hills. Looking down into your lap to consult a map or attempting to read a book while a passenger in a car is another cause of motion sickness.

Many 'cures' and preventatives for motion sickness have been proposed at various times. One which is both practical and effective is to simply look out of the window of the moving vehicle and to gaze into the distance towards the horizon in the direction in which you are moving. This helps to re-orient your inner sense of balance by reaffirming to your inner ear that you actually are moving. Fresh air blowing on your face can also be a relief.

Other cures for motion sickness rely on medication. Over-the-counter and prescription medications are readily available, eg. dramamine. Ginger is a mild anti-emetic and sucking on crystalised ginger or sipping ginger tea can help to relieve the nausea. Interestingly, many pharmacological treatments which are effective for nausea and vomiting in some medical conditions may not be effective for motion sickness. For example, metoclopramide and prochlorperazine, although widely used, are ineffective for motion-sickness prevention and treatment. The sedating anti-histamine medications such as promethazine, work quite well for motion sickness, although they can cause significant drowsiness.

Half the astronauts in the U.S. space program have suffered from space sickness, including Sen. Jake Garn, who made it his study project while a passenger on the space shuttle in 1985. The specially-designed space shuttle zero-gravity toilet has two settings: one for ordinary waste and another for vomit.

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• Frequently asked questions about vomiting