SAD is a type of major depressive disorder, and sufferers may exhibit any of the associated symptoms, such as feelings of hopelessness and worthlessness, thoughts of suicide, loss of interest in activities, withdrawal from social interaction, sleep and appetite problems, difficulty with concentrating and making decisions, decreased sex drive, a lack of energy, or agitation. Symptoms of winter SAD often include oversleeping or difficulty waking up in the morning, nausea, and a tendency to over eat, often with a craving for carbohydrates, which leads to weight gain. SAD is typically associated with winter depression, but springtime lethargy or other seasonal mood patterns are not uncommon. Although each individual case is different, in contrast to winter SAD, people who experience spring and summer depression may be more likely to show symptoms such as insomnia, decreased appetite and weight loss, and agitation or anxiety.

Hypomania is the signature characteristic of Bipolar II disorder. It is a state characterized by euphoria and/or an irritable mood. In order for an episode to qualify as hypomanic, the individual must also present three or more of the below symptoms, and last at least four consecutive days and be present most of the day, nearly every day

- Inflated self-esteem or grandiosity.

- Decreased need for sleep (e.g., feels rested after only 3 hours of sleep).

- More talkative than usual or pressure to keep talking.

- Flight of ideas or subjective experience that thoughts are racing.

- Distractibility (i.e., attention too easily drawn to unimportant or irrelevant external stimuli), as reported or observed.

- Increase in goal-directed activity (either socially, at work or school, or sexually) or psychomotor agitation.

- Excessive involvement in activities that have a high potential for painful consequences (e.g., engaging in unrestrained buying sprees, sexual indiscretions, or foolish business investments).

It is important to distinguish between hypomania and mania. Mania is generally greater in severity and impairs function, sometimes leading to hospitalization and in the most severe cases, psychosis. In contrast, hypomania usually increases functioning. For this reason, it is not uncommon for hypomania to go unnoticed. Often it is not until individuals are in a depressive episode that they seek treatment, and even then their history of hypomania may go undiagnosed. Even though hypomania may increase functioning, episodes need to be treated because they may precipitate a depressive episode.

Minor depressive disorder is very similar to major depressive disorder in the symptoms present. Generally, a person's mood is affected by thoughts and feelings of being sad or down on themself or by a loss of interest in nearly all activities. People can experience ups and downs in their life everyday where an event, action, stress or many other factors can affect their feelings on that day. However, depression occurs when those feelings of sadness persist for longer than a few weeks.

A person is considered to have minor depressive disorder if they experience 2 to 4 depressive symptoms during a 2-week period. The Diagnostic and Statistical Manual of Mental Disorders lists the major depressive symptoms. Depressed mood most of the day and/or loss of interest or pleasure in normal activities must be experienced by the individual to be considered to have minor depressive disorder. Without either of these two symptoms, the disorder is not classified as minor depressive disorder. Other depressive symptoms include significant weight loss or weight gain without trying to diet (an increase/decrease in appetite can provide clues as well), insomnia or hypersomnia, psychomotor agitation or psychomotor retardation, fatigue or loss of energy, and feelings of worthlessness or excessive guilt.

All of these signs can compound on each other to create the last major symptom group of minor depressive disorder: thoughts of death, suicidal thoughts, plans to commit suicide, or a suicide attempt.

Minor depressive disorder differs from major depressive disorder in the number of symptoms present with 5 or more symptoms necessary for a diagnosis of major depressive disorder. Both disorders require either depressed mood or loss of interest or pleasure in normal activities to be one of the symptoms and the symptoms need to be present for two weeks or longer. Symptoms also must be present for the majority of the length of a day and present for a majority of the days in the two-week period. Diagnosis can only occur if the symptoms cause "clinically significant distress or impairment". Dysthymia consists of the same depressive symptoms, but its main differentiable feature is its longer-lasting nature as compared to minor depressive disorder. Dysthymia was replaced in the DSM-5 by persistent depressive disorder, which combined dysthymia with chronic major depressive disorder.

Depressive mixed states occur when patients experience depression and non-euphoric, usually subsyndromal, hypomania at the same time. As mentioned previously, it is particularly difficult to diagnose BP-II when a patient is in this state.

In a mixed state, mood is depressed, but the following symptoms of hypomania present as well:

- Irritability

- Mental overactivity

- Behavioral overactivity

Mixed states are associated with greater levels of suicidality than non-mixed depression. Antidepressants may increase this risk.

"With seasonal pattern" is a specifier for "bipolar and related disorders", including bipolar I disorder and bipolar II disorder.

Most people with SAD experience major depressive disorder, but as many as 20% may have a bipolar disorder. It is important to discriminate between diagnoses because there are important treatment differences. In these cases, people who have the "With seasonal pattern" specifier may experience a depressive episode either due to major depressive disorder or as part of bipolar disorder during the winter and remit in the summer. Around 25% of patients with bipolar disorder may present with a depressive seasonal pattern, which is associated with bipolar II disorder, rapid cycling, eating disorders, and more depressive episodes. Gender displays distinct clinical characteristics associated to seasonal pattern: males present with more Bipolar II disorder and a higher number of depressive episodes, and females with rapid cycling and eating disorders.

Dysthymia, now known as persistent depressive disorder (PDD), is a mood disorder consisting of the same cognitive and physical problems as depression, with less severe but longer-lasting symptoms. The concept was coined by Robert Spitzer as a replacement for the term "depressive personality" in the late 1970s.

According to the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders, published in 1994 (DSM-IV), dysthymia is a serious state of chronic depression, which persists for at least two years (one year for children and adolescents). Dysthymia is less acute and severe than major depressive disorder. As dysthymia is a chronic disorder, sufferers may experience symptoms for many years before it is diagnosed, if diagnosis occurs at all. As a result, they may believe that depression is a part of their character, so they may not even discuss their symptoms with doctors, family members or friends.

Dysthymia often co-occurs with other mental disorders. A "double depression" is the occurrence of episodes of major depression in addition to dysthymia. Switching between periods of dysthymic moods and periods of hypomanic moods is indicative of cyclothymia, which is a mild variant of bipolar disorder.

In the DSM-5, dysthymia is replaced by persistent depressive disorder. This new condition includes both chronic major depressive disorder and the previous dysthymic disorder. The reason for this change is that there was no evidence for meaningful differences between these two conditions.

The term is from Ancient Greek , meaning bad state of mind.

Dysthymia characteristics include an extended period of depressed mood combined with at least two other symptoms which may include insomnia or hypersomnia, fatigue or low energy, eating changes (more or less), low self-esteem, or feelings of hopelessness. Poor concentration or difficulty making decisions are treated as another possible symptom. Mild degrees of dysthymia may result in people withdrawing from stress and avoiding opportunities for failure. In more severe cases of dysthymia, people may even withdraw from daily activities. They will usually find little pleasure in usual activities and pastimes. Diagnosis of dysthymia can be difficult because of the subtle nature of the symptoms and patients can often hide them in social situations, making it challenging for others to detect symptoms. Additionally, dysthymia often occurs at the same time as other psychological disorders, which adds a level of complexity in determining the presence of dysthymia, particularly because there is often an overlap in the symptoms of disorders. There is a high incidence of comorbid illness in those with dysthymia. Suicidal behavior is also a particular problem with persons with dysthymia. It is vital to look for signs of major depression, panic disorder, generalised anxiety disorder, alcohol and substance misuse and personality disorder.

Minor depressive disorder, also known as minor depression, is a mood disorder that does not meet the full criteria for major depressive disorder but at least two depressive symptoms are present for two weeks. These symptoms can be seen in many different psychiatric and mental disorders, which can lead to more specific diagnoses of an individual's condition. However, some of the situations might not fall under specific categories listed in the "Diagnostic and Statistical Manual of Mental Disorders". Minor depressive disorder is an example of one of these nonspecific diagnoses, as it is a disorder classified in the DSM-IV-TR under the category Depressive Disorder Not Otherwise Specified (DD-NOS). The classification of NOS depressive disorders is up for debate. Minor depressive disorder as a term was never an officially accepted term, but was listed in Appendix B of the DSM-IV-TR. This is the only version of the DSM that contains the term, as the prior versions and the most recent edition, DSM-5, does not mention it.

A person is considered to have minor depressive disorder if they experience 2 to 4 depressive symptoms, with one of them being either depressed mood or loss of interest or pleasure, during a 2-week period. The person must not have experienced the symptoms for 2 years and there must not have been one specific event that caused the symptoms to arise. Although not all cases of minor depressive disorder are deemed in need of treatment, some cases are treated similarly to major depressive disorder. This treatment includes cognitive behavioral therapy (CBT), anti-depressant medication, and combination therapy. A lot of research supports the notion that minor depressive disorder is an early stage of major depressive disorder, or that it is simply highly predictive of subsequent major depressive disorder.

Schizoaffective disorder is defined by "mood disorder-free psychosis" in the context of a long-term psychotic and mood disorder. Psychosis must meet criterion A for schizophrenia which may include delusions, hallucinations, disorganized speech, thinking or behavior and negative symptoms. Both delusions and hallucinations are classic symptoms of psychosis. Delusions are false beliefs which are strongly held despite evidence to the contrary. Beliefs should not be considered delusional if they are in keeping with cultural beliefs. Delusional beliefs may or may not reflect mood symptoms (for example, someone experiencing depression may or may not experience delusions of guilt). Hallucinations are disturbances in perception involving any of the five senses, although auditory hallucinations (or "hearing voices") are the most common. A lack of responsiveness or negative symptoms include alogia (lack of spontaneous speech), blunted affect (reduced intensity of outward emotional expression), avolition (loss of motivation), and anhedonia (inability to experience pleasure). Negative symptoms can be more lasting and more debilitating than positive symptoms of psychosis.

Mood symptoms are of mania, hypomania, mixed episode, or depression, and tend to be episodic rather than continuous. A mixed episode represents a combination of symptoms of mania and depression at the same time. Symptoms of mania include elevated or irritable mood, grandiosity (inflated self-esteem), agitation, risk-taking behavior, decreased need for sleep, poor concentration, rapid speech, and racing thoughts. Symptoms of depression include low mood, apathy, changes in appetite or weight, disturbances in sleep, changes in motor activity, fatigue, guilt or feelings of worthlessness, and suicidal thinking.

A person experiencing a depressive episode may have a marked loss or gain of weight (such as 5% of their body weight in one month) or a change in appetite.

Changes in appetite take on two manifestations: under- or over-eating.

In the first instance, some people never feel hungry, can go long periods without wanting to eat, or may forget to eat; if they do eat, a small amount of food may be sufficient. In children, failure to make expected weight gains may be counted towards this criteria. Under-eating is often associated with a melancholic type of depression.

In the second instance, some people tend toward an increase in appetite and may gain significant amounts of weight. They may crave certain types of food, such as sweets or carbohydrates. People with seasonal affective disorder (SAD) often crave foods high in carbohydrates. Over-eating is often associated with a type of depression called atypical depression.

Nearly every day, the person may sleep excessively, known as hypersomnia, or not enough, known as insomnia.

Insomnia is the most common type of sleep disturbance for people who are clinically depressed and is often associated with a melancholic type of depression. Symptoms of insomnia include trouble falling asleep, trouble staying asleep, and/or waking up too early in the morning.

Hypersomnia is a less common type of sleep disturbance. It may include sleeping for prolonged periods at night or increased sleeping during the daytime. The sleep may not be restful, and the person may feel sluggish despite many hours of sleep. This impacts their everyday activities and ability to focus at home or work. According to the United States National Library of Medicine, people with seasonal affective disorder (SAD) may sleep longer during the winter months. Hypersomnia is often associated with an atypical depression. Hypersomnia is not as common as insomnia and up to 40% of people exhibit hypersomnia from time to time.

Major depression significantly affects a person's family and personal relationships, work or school life, sleeping and eating habits, and general health. Its impact on functioning and well-being has been compared to that of other chronic medical conditions such as diabetes.

A person having a major depressive episode usually exhibits a very low mood, which pervades all aspects of life, and an inability to experience pleasure in activities that were formerly enjoyed. Depressed people may be preoccupied with, or ruminate over, thoughts and feelings of worthlessness, inappropriate guilt or regret, helplessness, hopelessness, and self-hatred. In severe cases, depressed people may have symptoms of psychosis. These symptoms include delusions or, less commonly, hallucinations, usually unpleasant. Other symptoms of depression include poor concentration and memory (especially in those with melancholic or psychotic features), withdrawal from social situations and activities, reduced sex drive, irritability, and thoughts of death or suicide. Insomnia is common among the depressed. In the typical pattern, a person wakes very early and cannot get back to sleep. Hypersomnia, or oversleeping, can also happen. Some antidepressants may also cause insomnia due to their stimulating effect.

A depressed person may report multiple physical symptoms such as fatigue, headaches, or digestive problems; physical complaints are the most common presenting problem in developing countries, according to the World Health Organization's criteria for depression. Appetite often decreases, with resulting weight loss, although increased appetite and weight gain occasionally occur. Family and friends may notice that the person's behavior is either agitated or lethargic. Older depressed people may have cognitive symptoms of recent onset, such as forgetfulness, and a more noticeable slowing of movements. Depression often coexists with physical disorders common among the elderly, such as stroke, other cardiovascular diseases, Parkinson's disease, and chronic obstructive pulmonary disease.

Depressed children may often display an irritable mood rather than a depressed mood, and show varying symptoms depending on age and situation. Most lose interest in school and show a decline in academic performance. They may be described as clingy, demanding, dependent, or insecure. Diagnosis may be delayed or missed when symptoms are interpreted as normal moodiness.

Schizoaffective disorder (SZA, SZD or SAD) is a mental disorder characterized by abnormal thought processes and deregulated emotions. The diagnosis is made when the person has features of both schizophrenia and a mood disorder—either bipolar disorder or depression—but does not strictly meet diagnostic criteria for either alone. The bipolar type is distinguished by symptoms of mania, hypomania, or mixed episode; the depressive type by symptoms of depression only. Common symptoms of the disorder include hallucinations, paranoid delusions, and disorganized speech and thinking. The onset of symptoms usually begins in young adulthood, currently with an uncertain lifetime prevalence because the disorder was redefined, but DSM-IV prevalence estimates were less than 1 percent of the population, in the range of 0.5 to 0.8 percent. Diagnosis is based on observed behavior and the person's reported experiences.

Genetics, neurobiology, early and current environment, behavioral, social, and experiential components appear to be important contributory factors; some recreational and prescription drugs may cause or worsen symptoms. No single isolated organic cause has been found, but extensive evidence exists for abnormalities in the metabolism of tetrahydrobiopterin (BH4), dopamine, and glutamic acid in people with schizophrenia, psychotic mood disorders, and schizoaffective disorder. People with schizoaffective disorder are likely to have co-occurring conditions, including anxiety disorders and substance use disorder. Social problems such as long-term unemployment, poverty and homelessness are common. The average life expectancy of people with the disorder is shorter than those without it, due to increased physical health problems from an absence of health promoting behaviors such as a sedentary lifestyle, and a higher suicide rate.

The mainstay of current treatment is antipsychotic medication combined with mood stabilizer medication or antidepressant medication, or both. There is growing concern by some researchers that antidepressants may increase psychosis, mania, and long-term mood episode cycling in the disorder. When there is risk to self or others, usually early in treatment, hospitalization may be necessary. Psychiatric rehabilitation, psychotherapy, and vocational rehabilitation are very important for recovery of higher psychosocial function. As a group, people with schizoaffective disorder diagnosed using DSM-IV and criteria have a better outcome than people with schizophrenia, but have variable individual psychosocial functional outcomes compared to people with mood disorders, from worse to the same. Outcomes for people with DSM-5 diagnosed schizoaffective disorder depend on data from prospective cohort studies, which haven't been completed yet.

In DSM-5 and ICD-10, schizoaffective disorder is in the same diagnostic class as schizophrenia, but not in the same class as mood disorders. The diagnosis was introduced in 1933, and its definition was slightly changed in the DSM-5, published in May 2013, because the DSM-IV schizoaffective disorder definition leads to excessive misdiagnosis. The changes made to the schizoaffective disorder definition were intended to make the DSM-5 diagnosis more consistent (or reliable), and to substantially reduce the use of the diagnosis. Additionally, the DSM-5 schizoaffective disorder diagnosis can no longer be used for first episode psychosis.

Psychotic symptoms are often missed in psychotic depression, either because patients do not think their symptoms are abnormal or they attempt to conceal their symptoms from others. On the other hand, psychotic depression may be confused with schizoaffective disorder. Due to overlapping symptoms, differential diagnosis includes also dissociative disorders.

Major depression frequently co-occurs with other psychiatric problems. The 1990–92 "National Comorbidity Survey" (US) reports that half of those with major depression also have lifetime anxiety and its associated disorders such as generalized anxiety disorder. Anxiety symptoms can have a major impact on the course of a depressive illness, with delayed recovery, increased risk of relapse, greater disability and increased suicide attempts. There are increased rates of alcohol and drug abuse and particularly dependence, and around a third of individuals diagnosed with ADHD develop comorbid depression. Post-traumatic stress disorder and depression often co-occur. Depression may also coexist with attention deficit hyperactivity disorder (ADHD), complicating the diagnosis and treatment of both. Depression is also frequently comorbid with alcohol abuse and personality disorders.

Depression and pain often co-occur. One or more pain symptoms are present in 65% of depressed patients, and anywhere from 5 to 85% of patients with pain will be suffering from depression, depending on the setting; there is a lower prevalence in general practice, and higher in specialty clinics. The diagnosis of depression is often delayed or missed, and the outcome can worsen if the depression is noticed but completely misunderstood.

Depression is also associated with a 1.5- to 2-fold increased risk of cardiovascular disease, independent of other known risk factors, and is itself linked directly or indirectly to risk factors such as smoking and obesity. People with major depression are less likely to follow medical recommendations for treating and preventing cardiovascular disorders, which further increases their risk of medical complications. In addition, cardiologists may not recognize underlying depression that complicates a cardiovascular problem under their care.

Individuals with psychotic depression experience the symptoms of a major depressive episode, along with one or more psychotic symptoms, including delusions and/or hallucinations. Delusions can be classified as mood congruent or incongruent, depending on whether or not the nature of the delusions is in keeping with the individual's mood state. Common themes of mood congruent delusions include guilt, persecution, punishment, personal inadequacy, or disease. Half of patients experience more than one kind of delusion. Delusions occur without hallucinations in about one-half to two-thirds of patients with psychotic depression. Hallucinations can be auditory, visual, olfactory (smell), or haptic (touch), and are congruent with delusional material. Affect is sad, not flat. Severe anhedonia, loss of interest, and psychomotor retardation are typically present.

To meet criteria for a major depressive episode, a patient must have 5 of these 9 symptoms nearly every day for at least 2 weeks.

1. Depressed or sad mood

2. Anhedonia (loss of interest in pleasurable activities)

3. Sleep disturbance (increased or decreased sleep)

4. Appetite disturbance (increased or decreased appetite) typically with weight change

5. Energy disturbance (increased or decreased energy/activity level), usually fatigue

6. Poor memory and/or concentration

7. Feelings of guilt or worthlessness

8. Psychomotor retardation or agitation (a change in mental and physical speed perceived by other people)

9. Thoughts of wishing you were dead; suicidal ideation or suicide attempts

Depression is a state of low mood and aversion to activity. It may be a normal reaction to occurring life events or circumstances, a symptom of a medical condition, a side effect of drugs or medical treatments, or a symptom of certain psychiatric syndromes, such as the mood disorders major depressive disorder and dysthymia. Depression in childhood and adolescence is similar to adult major depressive disorder, although young sufferers may exhibit increased irritability or aggressive and self-destructive behavior, rather than the all-encompassing sadness associated with adult forms of depression. Children who are under stress, experience loss, or have attention, learning, behavioral, or anxiety disorders are at a higher risk for depression. Childhood depression is often co-morbid with mental disorders outside of other mood disorders; most commonly anxiety disorder and conduct disorder. Depression also tends to run in families. Psychologists have developed different treatments to assist children and adolescents suffering from depression, though the legitimacy of the diagnosis of childhood depression as a psychiatric disorder, as well as the efficacy of various methods of assessment and treatment, remains controversial.

Depression is a state of a low mood and aversion to activity that can affect a person's thoughts, behavior, feelings, and sense of well-being. A depressed mood is a normal temporary reaction to life events such as loss of a loved one. It is also a symptom of some physical diseases and a side effect of some drugs and medical treatments. Depressed mood is also a symptom of some mood disorders such as major depressive disorder or dysthymia.

People with a depressed mood may be notably sad, anxious, or empty; they may also feel notably hopeless, helpless, dejected, or worthless. Other symptoms expressed may include senses of guilt, irritability, or anger. Further feelings expressed by these individuals may include feeling ashamed or an expressed restlessness. These individuals may notably lose interest in activities that they once considered pleasurable to family and friends or otherwise experience either a loss of appetite or overeating. Experiencing problems concentrating, remembering general facts or details, otherwise making decisions or experiencing relationship difficulties may also be notable factors in these individuals' depression and may also lead to their attempting or actually dying by suicide.

Expressed insomnia, excessive sleeping, fatigue, and vocalizing general aches, pains, and digestive problems and a reduced energy may also be present in individuals experiencing depression.

Late life depression refers to a major depressive episode occurring for the first time in an older person (usually over 50 or 60 years of age). Concurrent medical problems and lower functional expectations of elderly patients often obscure the degree of impairment. Typically, elderly patients with depression do not report depressed mood, but instead present with less specific symptoms such as insomnia, anorexia, and fatigue. Elderly persons sometimes dismiss less severe depression as an acceptable response to life stress or a normal part of aging.

Premenstrual dysphoric disorder (PMDD) is a severe form of premenstrual syndrome (PMS). Like PMS, premenstrual dysphoric disorder follows a predictable, cyclic pattern. Symptoms begin in the late luteal phase of the menstrual cycle (after ovulation) and end shortly after menstruation begins. On average, the symptoms last six days but can start up to two weeks before menses. The most intense symptoms occur two days before the start of menstrual blood flow through the first day of menstrual blood flow. The symptoms should cease shortly after the start of the menstrual period.

The symptoms in PMDD can be both physical and emotional with mood symptom being dominant. The most debilitating symptoms are emotional and include "irritability, depression, mood lability, anxiety, feelings of ‘loss of control’, difficulty concentrating and fatigue." The physical symptoms include "abdominal bloating, breast tenderness, headache and generalized aches."

Generalized anxiety disorder (GAD) is a common disorder, characterized by long-lasting anxiety that is not focused on any one object or situation. Those suffering from generalized anxiety disorder experience non-specific persistent fear and worry, and become overly concerned with everyday matters. Generalized anxiety disorder is "characterized by chronic excessive worry accompanied by three or more of the following symptoms: restlessness, fatigue, concentration problems, irritability, muscle tension, and sleep disturbance". Generalized anxiety disorder is the most common anxiety disorder to affect older adults. Anxiety can be a symptom of a medical or substance abuse problem, and medical professionals must be aware of this. A diagnosis of GAD is made when a person has been excessively worried about an everyday problem for six months or more. A person may find that they have problems making daily decisions and remembering commitments as a result of lack of concentration/preoccupation with worry. Appearance looks strained, with increased sweating from the hands, feet, and axillae, and they may be tearful, which can suggest depression. Before a diagnosis of anxiety disorder is made, physicians must rule out drug-induced anxiety and other medical causes.

In children GAD may be associated with headaches, restlessness, abdominal pain, and heart palpitations. Typically it begins around 8 to 9 years of age.

According to the DSM-IV, children must exhibit either a depressed mood or a loss of interest or pleasure in normal activities. These activities may include school, extracurricular activities, or peer interactions. Depressive moods in children can be expressed as being unusually irritable, which may be displayed by "acting out," behaving recklessly, or often reacting with anger or hostility. Children who do not have the cognitive or language development to properly express mood states can also exhibit their mood through physical complaints such as showing sad facial expressions (frowning) and poor eye contact. A child must also exhibit four other symptoms in order to be clinically diagnosed. However, according to the Omnigraphics "Health References Series: Depression Sourcebook, Third Edition", a more calculated evaluation must be given by a medical or mental health professional such as a physiologist or psychiatrist. Following the bases of symptoms, signs include, but are not limited to, an unusual change in sleep habits (for example, trouble sleeping or overly indulged sleeping hours); a significant amount of weight gain/loss by lack or excessive eating; experiencing aches/pains for no apparent reason that can found; and an inability to concentrate on tasks or activities. If these symptoms are present for a period of two weeks or longer, it is safe to make the assumption that the child, or anybody else for that matter, is falling into major depression.

The single largest category of anxiety disorders is that of specific phobias which includes all cases in which fear and anxiety are triggered by a specific stimulus or situation. Between 5% and 12% of the population worldwide suffer from specific phobias. Sufferers typically anticipate terrifying consequences from encountering the object of their fear, which can be anything from an animal to a location to a bodily fluid to a particular situation. Common phobias are flying, blood, water, highway driving, and tunnels. When people are exposed to their phobia, they may experience trembling, shortness of breath, or rapid heartbeat. People understand that their fear is not proportional to the actual potential danger but still are overwhelmed by it.

Premenstrual dysphoric disorder (PMDD) is a severe and disabling form of premenstrual syndrome affecting 3–8% of menstruating women. The disorder consists of a "cluster of affective, behavioral and somatic symptoms" that recur monthly during the luteal phase of the menstrual cycle. PMDD was added to the list of depressive disorders in the "Diagnostic and Statistical Manual of Mental Disorders" in 2013. The exact pathogenesis of the disorder is still unclear and is an active research topic. Treatment of PMDD relies largely on antidepressants that modulate serotonin levels in the brain via serotonin reuptake inhibitors as well as ovulation suppression using contraception.