The causes of PTSD are: Natural or human disasters, war, serious accident, witness of violent death of others, violent attack, being the victim of sexual abuse, rape, torture, terrorism or hostage taking.

Predisposing factors

The predisposing factors are: Personality traits and Previous history of Psychiatric illness.

Psychiatric consultation: Exploration of memories of the traumatic event, relief of associated symptoms and counseling.

Figures from the 1982 Lebanon war showed that with proximal treatment 90% of CSR casualties returned to their unit, usually within 72 hours. With rearward treatment only 40% returned to their unit. It was also found that treatment efficacy went up with the application of a variety of front line treatment principles versus just one treatment. In Korea, similar statistics were seen, with 85% of US battle fatigue casualties returned to duty within three days and 10% returned to limited duties after several weeks. Though these numbers seem to promote the claims that proximal PIE or BICEPS treatment is generally effective at reducing the effects of combat stress reaction, other data suggests that long term PTSD effects may result from the hasty return of affected individuals to combat. Both PIE and BICEPS are meant to return as many soldiers as possible to combat, and may actually have adverse effects on the long term health of service members who are rapidly returned to the front-line after combat stress control treatment. Although the PIE principles were used extensively in the Vietnam War, the post traumatic stress disorder lifetime rate for Vietnam veterans was 30% in a 1989 US study and 21% in a 1996 Australian study. In a study of Israeli Veterans of the 1973 Yom Kippur War, 37% of veterans diagnosed with CSR during combat were later diagnosed with PTSD, compared with 14% of control veterans.

Peacekeeping provides its own stresses because its emphasis on rules of engagement contains the roles for which soldiers are trained. Causes include witnessing or experiencing the following:

- Constant tension and threat of conflict.

- Threat of land mines and booby traps.

- Close contact with severely injured and dead people.

- Deliberate maltreatment and atrocities, possibly involving civilians.

- Cultural issues, e.g. male dominant attitudes towards women in different cultures.

- Separation and home issues.

- Risk of disease including HIV.

- Threat of exposure to toxic agents.

- Mission problems.

- Return to service.

Functional somatic syndromes may occur in 6 to 36% of the population.

A systematic review described improvement and occupational outcomes of people with CFS found that "the median full recovery rate was 5% (range 0–31%) and the median proportion of patients who improved during follow-up was 39.5% (range 8–63%). Return to work at follow-up ranged from 8 to 30% in the three studies that considered this outcome." ... "In five studies, a worsening of symptoms during the period of follow-up was reported in between 5 and 20% of patients." A good outcome was associated with less fatigue severity at baseline. Other factors were occasionally, but not consistently, related to outcome, including age at onset (5 of 16 studies), and attributing illness to a psychological cause and/or having a sense of control over symptoms (4 of 16 studies). Another review found that children have a better prognosis than adults, with 54–94% having recovered by follow-up compared to less than 10% of adults returning to pre-illness levels of functioning.

Genetic differences relating to toxicant metabolism pathways, such as polymorphisms and differences in expression in CYP2D6, NAT2, GSTM1, and PON1 and PON2, have been proposed as a cause for differences in susceptibility to MCS. Elevated nitric oxide and peroxynitrite (NO/ONOO-) could then cause the symptoms of MCS and several related conditions, including fibromyalgia, posttraumatic stress disorder, Gulf War syndrome, and chronic fatigue syndrome.

Treatment may involve investigation, reassurance and explanation, and possibly specialist treatment such as antidepressants or cognitive behavioral therapy.

Although in itself neither degenerative nor fatal, the chronic pain of fibromyalgia is pervasive and persistent. Most people with fibromyalgia report that their symptoms do not improve over time. An evaluation of 332 consecutive new people with fibromyalgia found that disease-related factors such as pain and psychological factors such as work status, helplessness, education, and coping ability had an independent and significant relationship to FM symptom severity and function.

People with British Gulf War syndrome who used personal organophosphate pesticides may be more likely to report the symptoms of MCS.

Fibromyalgia is estimated to affect 2–8% of the population. Female are affected about twice as often as male based on criteria as of 2014.

Fibromyalgia may not be diagnosed in up to 75% of affected people.

All ethnic groups and income levels are susceptible to the illness. The CDC states that CFS is "at least as common" in African Americans and Hispanics as Caucasians. A 2009 meta-analysis, however, showed that compared with the White American majority, African Americans and Native Americans have a higher risk of CFS, though it acknowledged that studies and data were limited. More women than men get CFS — between 60 and 85% of cases are women; however, there is some indication that the prevalence among men is underreported. The illness is reported to occur more frequently in persons between the ages of 40 and 59. CFS is less prevalent among children and adolescents than among adults.

Blood relatives of those who have CFS appear to be more predisposed. There is no direct evidence that CFS is contagious.

Psychological stress, childhood trauma, perfectionist personalities, old age, lower middle education, low physical fitness, preexisting psychological illness, and allergies may be risk factors for developing chronic fatigue syndrome. This has led some to believe that stress-related visceral responses underlie CFS. Pre-existing depressive and anxiety disorders, as well as high expectation of parents and family history were predisposing factors identified in another review.

People with CFS and their relatives tend to attribute their illness to physical causes (such as a virus or pollution) rather than to psychological causes. Such attributions are associated with increased symptoms and impairment, and worse outcomes over time.

The symptoms most commonly feigned include those associated with mild head injury, fibromyalgia, chronic fatigue syndrome, and chronic pain. Generally, malingerers complain of psychological disorders such as anxiety. Malingering may take the form of dishonest complaints of chronic whiplash pain from automobile accidents. The psychological symptoms experienced by survivors of disaster (post-traumatic stress disorder) are also faked by malingerers.

Individuals use a variety of methods to feign symptoms of illness. Some of these include harming oneself, trying to convince medical professionals one has a disease after learning about its details (such as symptoms) in medical textbooks, taking drugs that provoke certain symptoms common in some diseases, performing excess exercise to induce muscle strain or other physical types of ailments, and overdosing on drugs.

Panphobia, omniphobia, pantophobia, or panophobia is a vague and persistent dread of some unknown evil. Panphobia is not registered as a type of phobia in medical references.

Malingering is the fabricating of symptoms of mental or physical disorders for a variety of reasons such as financial compensation (often tied to fraud); avoiding school, work or military service; obtaining drugs; or as a mitigating factor for sentencing in criminal cases. It is not a medical diagnosis. Malingering is typically conceptualized as being distinct from other forms of excessive illness behaviour such as somatization disorder and factitious disorder, e.g., in DSM-5, although not all mental health professionals agree with this formulation.

Failure to detect actual cases of malingering imposes an economic burden on health care systems; workers compensation programs; and disability programs, e.g., Social Security Disability Insurance (United States) and U.S. Department of Veterans Affairs disability benefits. False attribution of malingering often harms genuine patients or claimants.

Shell shock is a phrase coined in World War I to describe the type of posttraumatic stress disorder many soldiers were afflicted with during the war (before PTSD itself was a term).

It is reaction to the intensity of the bombardment and fighting that produced a helplessness appearing variously as panic and being scared, or flight, an inability to reason, sleep, walk or talk.

During the War, the concept of shell shock was ill-defined. Cases of 'shell shock' could be interpreted as either a physical or psychological injury, or simply as a lack of moral fibre. The term "shell shock" is still used by the Veterans Administration to describe certain parts of PTSD but mostly it has entered into popular imagination and memory, and is often identified as the signature injury of the War.

In World War II and thereafter, diagnosis of 'shell shock' was replaced by that of combat stress reaction, a similar but not identical response to the trauma of warfare and bombardment.

There is no specific phobia in the DSM-5 which provides criteria for an all-encompassing fear of everything, though the defining symptom for Generalized Anxiety Disorder in this manual is "excessive anxiety and worry (apprehensive expectation) about a number of events or activities." Another very relatable state of mind is paranoia, in which one fears that unknown threats could, and most likely will, come from anyone, with distrust potentially leading to a loss of touch with reality. Delusional disorder is a more severe form of this type of disorder. Relevant academic literature may point to panphobia as merely a piece of such more complex states of mental disorder. Pseudoneurotic schizophrenia may be diagnosable in patients who, in addition to panphobia, also exhibit symptoms of "pananxiety", "panambivalence", and to a lesser extent, "chaotic sexuality". These persons differ from generalized anxiety sufferers in that they have "free-floating anxiety that rarely subsides" and are clinically diagnosable as having borderline personality disorder in the DSM-IV-TR. No significant changes related to this personality disorder were made in transitioning to the DSM-5, suggesting the diagnostic criteria are still appropriate.

The report of Da Costa shows that patients recovered from the more severe symptoms when removed from the strenuous activity or sustained lifestyle that caused them. A reclined position and forced bed rest was the most beneficial.

Other treatments evident from the previous studies were improving physique and posture, appropriate levels of exercise where possible, wearing loose clothing about the waist, and avoiding postural changes such as stooping, or lying on the left or right side, or the back in some cases, which relieved some of the palpitations and chest pains, and standing up slowly can prevent the faintness associated with postural or orthostatic hypotension in some cases.

Pharmacological intervention came in the form of digitalis, or "fox glove", which acts as a sodium-potassium ATPase inhibitor, increasing stroke volume and decreasing heart rate.

While the specific causes of sundowning have not been empirically proven, some evidence suggests that circadian rhythm disruption increases sundowning behaviors. In humans, sunset triggers a biochemical cascade that involves a reduction of dopamine levels and a shift towards melatonin production as the body prepares for sleep. In individuals with dementia, melatonin production may be decreased, which may interrupt other neurotransmitter systems.

Sundowning should be distinguished from delirium, and should be presumed to be delirium when it appears as a new behavioral pattern until a causal link between sunset and behavioral disturbance is established. Patients with established sundowning and no obvious medical illness may be suffering from impaired circadian regulation, or may be affected by nocturnal aspects of their institutional environment such as shift changes, increased noise, or reduced staffing (which leads to fewer opportunities for social interaction).

Although it is listed in the ICD-10 under "somatoform autonomic dysfunction", the term is no longer in common use by any medical agencies and has generally been superseded by more specific diagnoses.

The orthostatic intolerance observed by Da Costa has since also been found in patients diagnosed with chronic fatigue syndrome, postural orthostatic tachycardia syndrome (POTS) and mitral valve prolapse syndrome. In the 21st century, this intolerance is classified as a neurological condition. Exercise intolerance has since been found in many organic diseases.

During the early stages of World War I, soldiers from the British Expeditionary Force began to report medical symptoms after combat, including tinnitus, amnesia, headaches, dizziness, tremors, and hypersensitivity to noise. While these symptoms resembled those that would be expected after a physical wound to the brain, many of those reporting sick showed no signs of head wounds. By December 1914 as many as 10% of British officers and 4% of enlisted men were suffering from "nervous and mental shock".

The term "shell shock" came into use to reflect an assumed link between the symptoms and the effects of explosions from artillery shells. The term was first published in 1915 in an article in "The Lancet" by Charles Myers. Some 60–80% of shell shock cases displayed acute neurasthenia, while 10% displayed what would now be termed symptoms of conversion disorder, including mutism and fugue.

The number of shell shock cases grew during 1915 and 1916 but it remained poorly understood medically and psychologically. Some doctors held the view that it was a result of hidden physical damage to the brain, with the shock waves from bursting shells creating a cerebral lesion that caused the symptoms and could potentially prove fatal. Another explanation was that shell shock resulted from poisoning by the carbon monoxide formed by explosions.

At the same time an alternative view developed describing shell shock as an emotional, rather than a physical, injury. Evidence for this point of view was provided by the fact that an increasing proportion of men suffering shell shock symptoms had not been exposed to artillery fire. Since the symptoms appeared in men who had no proximity to an exploding shell, the physical explanation was clearly unsatisfactory.

In spite of this evidence, the British Army continued to try to differentiate those whose symptoms followed explosive exposure from others. In 1915 the British Army in France was instructed that:

However, it often proved difficult to identify which cases were which, as the information on whether a casualty had been close to a shell explosion or not was rarely provided.

It is thought that with the development of plaques and tangles associated with Alzheimer's disease there might be a disruption within the suprachiasmatic nucleus (SCN). The suprachiasmatic nucleus is associated with regulating sleep patterns by maintaining circadian rhythms, which are strongly associated with external light and dark cues. A disruption within the suprachiasmatic nucleus would seem to be an area that could cause the types of confusion that are seen in sundowning. However, finding evidence for this is difficult, as an autopsy is needed to definitively diagnose Alzheimer's in a patient. Once an Alzheimer's patient has died, they have usually surpassed the level of dementia and brain damage that would be associated with sundowning. This hypothesis is, however, supported by the effectiveness of melatonin, a natural hormone, to decrease behavioral symptoms associated with sundowning.

Another cause can be oral problems, like tooth decay with pain. When the time a meal is served comes close, a patient can show symptoms of sundowning. This cause is not widely recognized, however anticipation of food can increase dopamine levels, and dopamine and melatonin have an antagonistic relationship.

A study of certain aspects of motion sickness among medical transport attendants showed that the onset of the sopite syndrome is likely to occur independently of the mode of transportation; little difference was observed in the frequency of sopite symptoms for ground transport compared to air transport. Also, the length of time exposed to vehicular motion did not appear to affect the occurrence (or lack thereof) or severity of the sopite syndrome. No difference was observed in the incidence of the sopite syndrome for men versus women.

The sopite syndrome is likely a cumulative disorder. For instance, when a subject has the flu, a hangover may exacerbate the symptoms of the illness. A subject normally resistant to motion sickness may experience symptoms of motion sickness when also experiencing flu-like (or hangover-like) symptoms.

The sopite syndrome (; Latin: sopire, "to lay to rest, to put to sleep") is a neurological disorder that relates symptoms of fatigue, drowsiness, and mood changes to prolonged periods of motion. The sopite syndrome has been attributed to motion-induced drowsiness such as that experienced by a baby when rocked. Researchers Graybiel and Knepton at the Naval Aerospace Medical Research Laboratory first used the term "the sopite syndrome", in 1976, to refer to the sometimes sole manifestation of motion sickness, though other researchers have referred to it as "Sopite syndrome."

The most common causes of myalgia by injury are: sprains and strains.