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.

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.

Space adaptation syndrome (SAS) or space sickness is a condition experienced by around half of space travelers during adaptation to weightlessness. It is related to motion sickness, as the vestibular system adapts to weightlessness.

Simulator sickness is a subset of motion sickness that is typically experienced by pilots who undergo training for extended periods of time in flight simulators. Due to the spatial limitations imposed on these simulators, perceived discrepancies between the motion of the simulator and that of the vehicle can occur and lead to simulator sickness.

It is similar to motion sickness in many ways, but occurs in simulated environments and can be induced without actual motion. Symptoms of simulator sickness include discomfort, apathy, drowsiness, disorientation, fatigue, vomiting, and many more.

These symptoms can reduce the effectiveness of simulators in flight training and result in systematic consequences such as decreased simulator use, compromised training, ground safety, and flight safety. Pilots are less likely to want to repeat the experience in a simulator if they have suffered from simulator sickness and hence can reduce the number of potential users. It can also compromise training in two safety-critical ways:

1. It can distract the pilot during training sessions.

2. It can cause the pilot to adopt certain counterproductive behaviors to prevent symptoms from occurring.

Simulator sickness can also have post-training effects that can compromise safety after the simulator session, such as when the pilots drive away from the facility or fly while experiencing symptoms of simulator sickness.

Space motion sickness is caused by changes in g-forces, which affect spatial orientation in humans. According to "Science Daily", "Gravity plays a major role in our spatial orientation. Changes in gravitational forces, such as the transition to weightlessness during a space voyage, influence our spatial orientation and require adaptation by many of the physiological processes in which our balance system plays a part. As long as this adaptation is incomplete, this can be coupled to motion sickness (nausea), visual illusions and disorientation."

Modern motion-sickness medications can counter space sickness but are rarely used because it is considered better to allow space travelers to adapt naturally over the first day or two than to suffer the drowsiness and other side effects of medication. However, transdermal dimenhydrinate anti-nausea patches are typically used whenever space suits are worn because vomiting into a space suit could be fatal, as it could obscure vision or block airflow. Space suits are generally worn during launch and landing by NASA crew members and always for extra-vehicular activities (EVAs). EVAs are consequently not usually scheduled for the first days of a mission to allow the crew to adapt, and transdermal dimenhydrinate patches are typically used as an additional backup measure.

Common symptoms of airsickness include:

Nausea, vomiting, vertigo, loss of appetite, cold sweating, skin pallor, difficulty concentrating, confusion, drowsiness, headache, and increased fatigue.

Severe airsickness may cause a person to become completely incapacitated.

Airsickness is a sensation which is induced by air travel. It is a specific form of motion sickness, and is considered a normal response in healthy individuals. Airsickness occurs when the central nervous system receives conflicting messages from the body (including the inner ear, eyes and muscles) affecting balance and equilibrium.

The inner ear is particularly important in the maintenance of balance and equilibrium because it contains sensors for both angular (rotational) and linear motion. Airsickness is usually a combination of spatial disorientation, nausea and vomiting.

The sopite syndrome has been associated with visually-induced and vestibular motion sickness. Other factors associated with drowsiness such as darkness or physical fatigue may intensify the effects of motion-induced sleepiness. The sopite syndrome may occur with little motional stimulus (though the greatest effects tend to be observed in subjects who have been exposed for longer periods of time), and often persists for a time after the motional stimulus has ceased.

The symptoms and signs, as described by physician John Caius and others, were as follows: the disease began very suddenly with a sense of apprehension, followed by cold shivers (sometimes very violent), giddiness, headache, and severe pains in the neck, shoulders and limbs, with great exhaustion. After the cold stage, which might last from half an hour to three hours, the hot and sweating stage followed. The characteristic sweat broke out suddenly without any obvious cause. Accompanying the sweat, or after, was a sense of heat, headache, delirium, rapid pulse, and intense thirst. Palpitation and pain in the heart were frequent symptoms. No skin eruptions were noted by observers including Caius. In the final stages, there was either general exhaustion and collapse, or an irresistible urge to sleep, which Caius thought to be fatal if the patient was permitted to give way to it. One attack did not offer immunity, and some people suffered several bouts before dying. The disease tended to occur in summer and early autumn.

The effects of the sopite syndrome may range from minor physical inconveniences to hazardous conditions. Persons who operate automobiles, airplanes, et cetera, may experience impaired motor function due to the motions of the vehicle. These impairments often result in a decreased attention span; persons who consider themselves well-rested may still succumb to drowsiness at inopportune moments. The sopite syndrome may therefore contribute to motor vehicle accidents in which automobile operators fall asleep at the wheel. However, the sopite syndrome itself does not directly result in death.

A subject experiencing the sopite syndrome on a frequent basis may increase the number of hours spent sleeping by fifty percent. A study of motion sickness occurrences in workers on an offshore oil vessel showed a large majority of participants experienced mild symptoms of fatigue. Many participants also experienced severe sleep disturbances. These symptoms were associated with impaired task performance.

About 66% of women have both nausea and vomiting while 33% have just nausea.

The Simulator Sickness Questionnaire (SSQ) is currently the standard for measuring simulator sickness. The SSQ was developed based upon 1,119 pairs of pre-exposure/post-exposure scores from data that were collected and reported earlier. These data were collected from 10 Navy flight simulators representing both fixed-wing and rotary-wing aircraft. The simulators selected were both 6-DOF motion and fixed-base models, and also represented a variety of visual display technologies. The SSQ was developed and validated with data from pilots who reported to simulator training healthy and fit.

The SSQ is a self-report symptom checklist. It includes 16 symptoms that are associated with simulator sickness. Participants indicate the level of severity of the 16 symptoms that they are experiencing currently. For each of the 16 symptoms there are four levels of severity (none, slight, moderate, severe). The SSQ provides a Total Severity score as well as scores for three subscales (Nausea, Oculomotor, and Disorientation). The Total Severity score is a composite created from the three subscales. It is the best single measure because it provides an index of the overall symptoms. The three subscales provide diagnostic information about particular symptom categories:

- Nausea subscale is made up of symptoms such as increased salivation, sweating, nausea, stomach awareness, and burping.

- Oculomotor subscale includes symptoms such as fatigue, headache, eyestrain, and difficulty focusing.

- Disorientation subscale is composed of symptoms such as vertigo, dizzy (eyes open), dizzy (eyes closed), and blurred vision.

The three subscales are not orthogonal to one another. There is a general factor common to all of them. Nonetheless, the subscales provide differential information about participants' experience of symptoms and are useful for determining the particular pattern of discomfort produced by a given simulator. All scores have as their lowest level a natural zero (no symptoms) and increase with increasing symptoms reported.

Morning sickness, also called nausea and vomiting of pregnancy (NVP), is a symptom of pregnancy that involves nausea or vomiting. Despite the name, nausea or vomiting can occur at any time during the day. Typically these symptoms occur between the 4th and 16th week of pregnancy. About 10% of women still have symptoms after the 20th week of pregnancy. A severe form of the condition is known as hyperemesis gravidarum and results in weight loss.

The cause of morning sickness is unknown but may be related to changing levels of the hormone human chorionic gonadotrophin. Some have proposed that it may be useful from an evolutionary point of view. Diagnosis should only occur after other possible causes have been ruled out. Abdominal pain, fever, or headaches are typically not present in morning sickness.

Taking prenatal vitamins before pregnancy may decrease the risk. Specific treatment other than a bland diet may not be required for mild cases. If treatment is used the combination of doxylamine and pyridoxine is recommended initially. There is limited evidence that ginger may be useful. For severe cases that have not improved with other measures methylprednisolone may be tried. Tube feeding may be required in women who are losing weight.

Morning sickness affects about 70-80% of all pregnant women to some extent. About 60% of women have vomiting. Hyperemesis gravidarum occurs in about 1.6% of pregnancies. Morning sickness can negatively affect quality of life, result in decreased ability to work while pregnant, and result in health care expenses. Generally mild to moderate cases have no effect on the baby. Most severe cases also have normal outcomes. Some women choose to have an abortion due to the severity of symptoms. Complications such as Wernicke encephalopathy or esophageal rupture may occur but are very rare.

While bubbles can form anywhere in the body, DCS is most frequently observed in the shoulders, elbows, knees, and ankles. Joint pain ("the bends") accounts for about 60% to 70% of all altitude DCS cases, with the shoulder being the most common site. Neurological symptoms are present in 10% to 15% of DCS cases with headache and visual disturbances being the most common symptom. Skin manifestations are present in about 10% to 15% of cases. Pulmonary DCS ("the chokes") is very rare in divers and has been observed much less frequently in aviators since the introduction of oxygen pre-breathing protocols. The table below shows symptoms for different DCS types.

Acrophobia (from the , "ákron", meaning "peak, summit, edge" and , "phóbos", "fear") is an extreme or irrational fear or phobia of heights, especially when one is not particularly high up. It belongs to a category of specific phobias, called space and motion discomfort, that share both similar causes and options for treatment.

Most people experience a degree of natural fear when exposed to heights, known as the fear of falling. On the other hand, those who have little fear of such exposure are said to have a head for heights. A head for heights is advantageous for those hiking or climbing in mountainous terrain and also in certain jobs e.g. steeplejacks or wind turbine mechanics.

Acrophobia sufferers can experience a panic attack in high places and become too agitated to get themselves down safely. Approximately 2–5% of the general population suffers from acrophobia, with twice as many women affected as men.

Although onset of DCS can occur rapidly after a dive, in more than half of all cases symptoms do not begin to appear for at least an hour. In extreme cases, symptoms may occur before the dive has been completed. The U.S. Navy and Technical Diving International, a leading technical diver training organization, have published a table that documents time to onset of first symptoms. The table does not differentiate between types of DCS, or types of symptom.

Sweating sickness, also known as "English sweating sickness" or "English sweate" (), was a mysterious and highly contagious disease that struck England, and later continental Europe, in a series of epidemics beginning in 1485. The last outbreak occurred in 1551, after which the disease apparently vanished. The onset of symptoms was dramatic and sudden, death often occurring within hours. Although its cause remains unknown, it has been suggested that an unknown species of hantavirus was responsible for the outbreak.

Taravana is a disease often found among Polynesian island natives who habitually dive deep without breathing apparatus many times in close succession, usually for food or pearls. These free-divers may make 40 to 60 dives a day, each of 30 or 40 metres (100 to 140 feet).

Taravana seems to be decompression sickness. The usual symptoms are vertigo, nausea, lethargy, paralysis and death. The word "taravana" is Tuamotu Polynesian for "to fall crazily".

Taravana is also used to describe someone who is "crazy because of the sea".

Ghost sickness is a cultural belief among some traditional indigenous peoples in North America, notably the Navajo, and some Muscogee and Plains cultures, as well as among Polynesian peoples. People who are preoccupied and/or consumed by the deceased are believed to suffer from ghost sickness. Reported symptoms can include general weakness, loss of appetite, suffocation feelings, recurring nightmares, and a pervasive feeling of terror. The sickness is attributed to ghosts () or, occasionally, to witches or witchcraft. Children are thought to be especially at risk of being affected because they are not as attached to their new bodies.

Anticipatory anxiety of being out of control and overwhelmed can prevent a person from planning to travel by air. The thought of an upcoming flight can cause great distress, particularly when compelled to travel by air. The most extreme manifestations can include panic attacks or vomiting at the mere sight or mention of an aircraft or air travel.

Claustrophobia is typically thought to have two key symptoms: fear of restriction and fear of suffocation. A typical claustrophobic will fear restriction in at least one, if not several, of the following areas: small rooms, locked rooms, MRI or CAT scan apparatus, cars, airplanes, trains, tunnels, underwater caves, cellars, elevators and caves. Additionally, the fear of restriction can cause some claustrophobia to fear trivial matters such as sitting in a haircutter's chair or waiting in line at a grocery store simply out of a fear of confinement to a single space. Another possible site for claustrophobic attacks is a dentist's chair, particularly during dental surgery; in that scenario, the fear is not of pain, but of being confined.

Often, when confined to an area, claustrophobics begin to fear suffocation, believing that there may be a lack of air in the area to which they are confined.

Headaches are the primary symptom used to diagnose altitude sickness, although a headache is also a symptom of dehydration. A headache occurring at an altitude above a pressure of combined with any one or more of the following symptoms, may indicate altitude sickness:

Claustrophobia is the fear of having no escape, and being closed into a small space. It is typically classified as an anxiety disorder and often times results in a rather severe panic attack. It is also confused sometimes with Cleithrophobia (the fear of being trapped).

Traditionally, acrophobia has been attributed, like other phobias, to conditioning or a traumatic experience. Recent studies have cast doubt on this explanation; a fear of falling, along with a fear of loud noises, is one of the most commonly suggested inborn or "non-associative" fears. The newer non-association theory is that a fear of heights is an evolved adaptation to a world where falls posed a significant danger. The degree of fear varies and the term phobia is reserved for those at the extreme end of the spectrum. Researchers have argued that a fear of heights is an instinct found in many mammals, including domestic animals and humans. Experiments using visual cliffs have shown human infants and toddlers, as well as other animals of various ages, to be reluctant in venturing onto a glass floor with a view of a few meters of apparent fall-space below it. While an innate cautiousness around heights is helpful for survival, an extreme fear can interfere with the activities of everyday life, such as standing on a ladder or chair, or even walking up a flight of stairs.

A possible contributing factor is a dysfunction in maintaining balance. In this case the anxiety is both well founded and secondary. The human balance system integrates proprioceptive, vestibular and nearby visual cues to reckon position and motion. As height increases, visual cues recede and balance becomes poorer even in normal people. However, most people respond by shifting to more reliance on the proprioceptive and vestibular branches of the equilibrium system.

An acrophobic, however, continues to over-rely on visual signals whether because of inadequate vestibular function or incorrect strategy. Locomotion at a high elevation requires more than normal visual processing. The visual cortex becomes overloaded resulting in confusion. Some proponents of the alternative view of acrophobia warn that it may be ill-advised to encourage acrophobics to expose themselves to height without first resolving the vestibular issues. Research is underway at several clinics.

Fear of flying is a fear of being on an airplane (aeroplane), or other flying vehicle, such as a helicopter, while in flight. It is also referred to as flying phobia, flight phobia, aviophobia or aerophobia (although the last also means a fear of drafts or of fresh air).

Fear of flying may be a distinct phobia in itself, or it may be an indirect combination of one or more other disorders, such as claustrophobia (a phobia of being restricted, confined, or unable to escape) or acrophobia (anxiety or dread of being at a great height). It may have other causes as well, such as agoraphobia (especially the type associated with having a panic attack in a place they can't escape from). It is a symptom rather than a disease, and different causes may bring it about in different individuals.

This phobia receives more attention than most other phobias because air travel is often difficult for people to avoid—especially in professional contexts—and because it is common, affecting a significant minority of the population. Inability to maintain emotional control when aloft may prevent a person from going on vacations or visiting family and friends, and it can cripple the career of a businessperson by preventing them from traveling on work-related business.