Motion sickness occurs due to a difference between actual and expected motion. Symptoms commonly include nausea, vomiting, cold sweat, headache, dizziness, tiredness, loss of appetite, and increased salivation. Complications may rarely include dehydration, electrolyte problems, or a lower esophageal tear. The cause of motion sickness is either real or perceived motion. This may include car travel, air travel, sea travel, space travel, or reality simulation. Risk factors include pregnancy, migraines, and Ménière's disease. The diagnosis is based on symptoms. Treatment may include behavioral measures or medications. Behavioral measures include keeping the head still and focusing on the horizon. Three types of medications are useful: antimuscarinics such as scopolamine, H1 antihistamines such as dimenhydrinate, and amphetamines such as dexamphetamine. Side effects, however, may limit the use of medications. A number of medications used for nausea (antiemetics) such as ondansetron are not effective for motion sickness. Many people can be affected with sufficient motion and nearly everyone will experience motion sickness at least once in their lifetime. Susceptibility, however, is variable, with about one-third of the population being susceptible while other people can be affected only under very extreme conditions. Women can be more easily affected than men. Motion sickness has been described since at least the time of Homer (c. eighth century BC).
Signs and symptoms Signs and symptoms commonly include nausea, vomiting, cold sweat, headache, dizziness, tiredness, loss of appetite, and increased salivation. Occasionally, tiredness can last for hours to days after an episode of motion sickness, known as "sopite syndrome". Rarely severe symptoms such as the inability to walk, ongoing vomiting, or social isolation may occur while rare complications may include dehydration, electrolyte problems, or a lower esophageal tear from severe vomiting.
Cause Motion sickness can be divided into three categories:
Motion sickness caused by motion that is felt but not seen Motion sickness caused by motion that is seen but not felt Motion sickness that occurs when both systems detect motion, but they do not correspond
Motion felt but not seen In these cases, motion is sensed by the vestibular system and hence the motion is felt, but no motion or little motion is detected by the visual system.
Carsickness
Carsickness is quite common and may be caused by reading a map, a book, or a small screen during travel. If someone is looking at a stationary object within a moving vehicle, such as a magazine, their eyes will inform their brain that what they are viewing is not moving. Their inner ears, however, will contradict this by sensing the motion of the vehicle. Alternatively, carsickness may occur when the vestibular system senses stillness but the eyes see motion. In the early 20th century, Austro-Hungarian scientist Róbert Bárány observed the back-and-forth movement of the eyes of railroad passengers as they looked out the side windows at the scenery whipping by. He called this "railway nystagmus", also known as "optokinetic nystagmus". His findings were published in the journal Laeger, 83:1516, Nov.17, 1921.
Airsickness
Airsickness is essentially the same as carsickness, and is considered a normal response in healthy individuals. An airplane may bank and tilt sharply, and unless passengers are looking outside a window, they are likely to see only the stationary interior of the plane, especially during flights at night. Another factor is that while in flight, the view out of windows may be blocked by clouds, preventing passengers from seeing the moving ground or passing clouds.
Seasickness Like airsickness, seasickness is essentially the same as carsickness, though the motion of a watercraft tends to be more regular. It is typically brought on by the rocking motion of the craft or movement while the craft is immersed in water. As with airsickness, it can be difficult to visually detect motion even if one looks outside the boat since water does not offer fixed points with which to visually judge motion. Poor visibility conditions, such as fog, may worsen seasickness. The greatest contributor to seasickness is the tendency for people affected by the rolling or surging motions of the craft to seek refuge below decks, where they are unable to relate themselves to the boat's surroundings and consequent motion. Some people with carsickness are resistant to seasickness and vice versa. Adjusting to the craft's motion at sea is called "gaining one's sea legs"; it can take a significant portion of the time spent at sea after disembarking to regain a sense of stability "post-sea legs".
Centrifuge motion sickness Rotating devices such as centrifuges used in astronaut training and amusement park rides such as the Rotor, Mission: Space, and the Gravitron can cause motion sickness in many people. While the interior of the centrifuge does not appear to move, one will experience a sense of motion. In addition, centrifugal force can cause the vestibular system to give one the sense that downward is in the direction away from the center of the centrifuge rather than the true downward direction.
Dizziness due to spinning When one spins and stops suddenly, fluid in the inner ear continues to rotate, causing a sense of continued spinning while one's visual system no longer detects motion.
Virtual reality
Usually, VR programs would detect the motion of the user's head and adjust the rotation of the vision to avoid dizziness. However, in some cases, such as system lagging or software crashing, this could cause lags in the screen updates. In such cases, even some small head motions could trigger motion sickness by the defense mechanism mentioned below: the inner ear transmits to the brain that it senses motion, but the eyes tell the brain that everything is still.
Virtual reality to reverse motion sickness
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