Motion sickness is a condition in which a disagreement exists between visually perceived movement and the vestibular system's sense of movement. Depending on the cause, it can also be referred to as seasickness, car sickness, simulation sickness or airsickness.

Dizziness, fatigue and nausea are the most common symptoms of motion sickness. Sopite syndrome, in which a person feels fatigue or tiredness, is also associated with motion sickness. "Nausea" in Greek means seasickness ("naus" means ship). If the motion causing nausea is not resolved, the sufferer will usually vomit. Vomiting often will not relieve the feeling of weakness and nausea, which means the person might continue to vomit until the cause of the nausea is treated.

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.

Symptoms most frequently reported include a persistent sensation of motion usually described as rocking, swaying, or bobbing, disequilibrium with difficulty maintaining balance; it is seldom accompanied by a true spinning vertigo. Chronically fatigued, sufferers can become fatigued quickly with minimal exertion and experience neck and back pain. Other common symptoms include difficulty concentrating or inability to multitask, visual intolerance of busy patterns, headaches and/or migraine headaches, and ear pain or fullness.

Fluctuations in weather, in particular barometric pressure, also affect suffers. Many have photo-sensitivity and find it more difficult to walk in the dark as well as other sensitivities to strong smells including chemical smells. Cognitive impairment ("brain fog") includes an inability to recall words, short term memory loss, an inability to multi-task, misspelling and mispronunciation of words. MdDS sufferers report they are unable to use a computer for any length of time due to the visual overstimulation, and some are even unable to watch television.

The condition may be masked by a return to motion such as in a car, train, plane, or boat; however, once the motion ceases, the symptoms rebound or return, often at much higher levels than when the journey first commenced. Symptoms can be increased by stress, lack of sleep, crowds, flickering lights, loud sounds, fast or sudden movements, enclosed areas or busy patterns.

MdDS sufferers can sleep up to 12 or more hours a day, depending on their symptom levels. Research reveals MdDS is not migraine related and many sufferers have never had migraine symptoms prior to the onset of the disorder. However, for some MdDS sufferers there maybe have been a correlation between migraine and some pathophysiological overlap or even some other precipitating illness.

The symptoms of MdDS may be extremely debilitating and fluctuate high and low on a daily basis; it greatly affects the working capacity of sufferers with many having to relinquish work; it also limits most other daily and social activities. Sufferers can have low quality of life in both the physical and emotional realms, comparable to people who have multiple sclerosis.

Mal de debarquement (or mal de débarquement) syndrome (MdDS, or common name disembarkment syndrome) is a neurological condition usually occurring after a cruise, aircraft flight, or other sustained motion event. The phrase "mal de débarquement" is French for "sickness from disembarkation".

MdDS is typically diagnosed by a neurologist or an ear nose & throat specialist when a person reports a persistent rocking, swaying, or bobbing feeling (though they are not necessarily rocking). This usually follows a cruise or other motion experience. Because most vestibular testing proves to be negative, doctors may be baffled as they attempt to diagnose the syndrome. A major diagnostic indicator is that most patients feel better while driving or riding in a car, i.e.: while in passive motion. MdDS is unexplained by structural brain or inner ear pathology and most often corresponds with a motion trigger, although it can occur spontaneously. This differs from the very common condition of "land sickness" that most people feel for a short time after a motion event such as a boat cruise, aircraft ride, or even a treadmill routine which may only last minutes to a few hours. The syndrome has recently received increased attention due to the number of people presenting with the condition and more scientific research has commenced to determine what triggers MdDS and how to cure it.

Problems with balance can occur when there is a disruption in any of the vestibular, visual, or proprioceptive systems. Abnormalities in balance function may indicate a wide range of pathologies from causes like inner ear disorders, low blood pressure, brain tumors, and brain injury including stroke.

Many different terms are often used for dizziness, including lightheaded, floating, woozy, giddy, confused, helpless, or fuzzy. Vertigo, Disequilibrium and pre-syncope are the terms in use by most physicians and have more precise definitions.

Vertigo

Vertigo is the sensation of spinning or having the room spin about you. Most people find vertigo very disturbing and report associated nausea and vomiting.

Disequilibrium

Disequilibrium is the sensation of being off balance, and is most often characterized by frequent falls in a specific direction. This condition is not often associated with nausea or vomiting.

Presyncope

Pre-syncope is a feeling of lightheadedness or simply feeling faint. Syncope, by contrast, is actually fainting. A circulatory system deficiency, such as low blood pressure, can contribute to a feeling of dizziness when one suddenly stands up.

Problems in the skeletal or visual systems, such as arthritis or eye muscle imbalance, may also cause balance problems.

When balance is impaired, an individual has difficulty maintaining upright orientation. For example, an individual may not be able to walk without staggering, or may not even be able to stand. They may have falls or near-falls. The symptoms may be recurring or relatively constant. When symptoms exist, they may include:

- A sensation of dizziness or vertigo.

- Lightheadedness or feeling woozy.

- Problems reading and difficulty seeing.

- Disorientation.

Some individuals may also experience nausea and vomiting, diarrhea, faintness, changes in heart rate and blood pressure, fear, anxiety, or panic. Some reactions to the symptoms are fatigue, depression, and decreased concentration. The symptoms may appear and disappear over short time periods or may last for a longer period.

Cognitive dysfunction (disorientation) may occur with vestibular disorders. Cognitive deficits are not just spatial in nature, but also include non-spatial functions such as object recognition memory. Vestibular dysfunction has been shown to adversely affect processes of attention and increased demands of attention can worsen the postural sway associated with vestibular disorders. Recent MRI studies also show that humans with bilateral vestibular damage undergo atrophy of the hippocampus which correlates with their degree of impairment on spatial memory tasks.