Abnormalities in feelings, thinking, and behaviors are referred to as mental disorders. Mental disorders are extremely common in Americans. In fact, based on the diagnostic criteria for mental disorders, approximately 46% of Americans have some type of mental disorder. These mental disorders include anxiety disorders, depression, behavioral disorders, thought disorders, and substance-abuse disorders.

Common Types of Mental Disorders

1. Anxiety Disorders 

In the patients diagnosed with an anxiety disorder, he/she must be unable to respond appropriately to situations, they are unable to control their response, or their anxiety gets in the way of their normal day-to-day functions. Anxiety disorders manifest as fear and trepidation, as well as physical signs of uneasiness and anxiety that are characterized by an increased heart rate and perspiration. Anxiety disorders are further categorized based on their triggers. GAD (generalized anxiety disorder), PTSD (post-traumatic stress disorder), OCD (obsessive compulsive disorder), social anxiety disorder, panic disorder, and phobias are a few types of anxiety disorders. Some of these anxiety disorders are explored in detail below.

• Phobias: Phobia is the term used to describe an irrational and extreme fear of a situation or an object. There are many types of phobias, including the fear of spiders (arachnophobia), the fear of being up high (acrophobia), the fear of being away from home (agoraphobia), etc.
• Social anxiety disorder: The fear of being involved in social interactions is characteristic of social anxiety disorders. A good example of this is when a person has to give a speech.
• Generalized anxiety disorder (GAD): About 10% of the population suffers from GAD, making it a commonly diagnosed anxiety disorder. People suffering with this disorder tend to be extreme worriers about multiple aspects of their lives, such as their family, money, and their future. They may also have non-specific worries and anxieties.
• Panic disorder: Panic disorders are typified by frequent episodes of severe, unexpected, incapacitating anxiety attacks, also known as panic attacks. These panic attacks may include symptoms such as an accelerated heart beat, breathlessness, nausea, and an inability to think clearly. The diagnosis of panic disorder is dependent upon the person who may be worried about experiencing a panic attack or worried about the panic attack being the symptoms of a medical condition, like a heart attack.

2. Behavioral Disorders

Behavioral disorder is the catch-all term used to refer to the inability to display acceptable behaviors for a given situation. The one that you are probably most familiar with is ADHD (attention deficit hyperactivity disorder) because it is very commonly diagnosed among so many types of mental disorders. Because ADHD was initially more commonly diagnosed in boys, it was thought to be a disorder of boys; however, ADHD is also frequently diagnosed in girls. Interestingly, about half of the children that are diagnosed with ADHD in childhood continue to display symptoms in adulthood. The symptoms of ADHD include the inability to pay attention in addition to hyperactive and impulsive behaviors.

3. Mood Disorders

Mood disorders or affective disorders are classified as the constant feeling of being sad or periods of extreme happiness, or going back and forth between feeling overly happy to overly sad. Typically a person that is diagnosed with depression experiences feelings of sadness that prohibit them from functionally normally. These feelings of sadness last longer than would be expected given the situation. Depressive disorders can be further categorized as bipolar disorders, dysthymia, or major depression.

• Major depression: In order to be diagnosed with major depression, the individual must feel depressed for most of the day and for most days over at least a two-week time period. Additionally, they may experience symptoms such as changes in appetite and weight, irritability, loss of interest and motivation for their usual activities, hopelessness, and in some cases thoughts, plans or attempts to cause harm to themselves. Some women may experience depression after having a child, in which case it is called postpartum depression. The duration of postpartum depression can vary from weeks to months.
• Dysthymia: In general, symptoms of dysthymia are milder compared to the symptoms of major depression. The symptoms of dysthymia usually continue consistently for more than one year in young adults and children, and for over two years in adults.
• Bipolar disorder: In the United States, over 1% of adults or up to 4 million people have been diagnosed with bipolar disorder. Bipolar disorder is sometimes referred to as manic depression. It is characterized by extreme changes in mood, recurring depressive episodes, and at least a single manic episode.

4. Psychotic Disorders

People diagnosed with psychotic disorders experience a warped sense of thinking and awareness. This is typified by auditory or visual hallucinations and delusions. The person believes these delusions to be true, although there is an abundance of evidence to indicate that they are not. A diagnosis of schizophrenia is an example of a psychotic disorder.

5. Eating Disorders

The most common eating disorders are binge eating, bulimia nervosa, and anorexia nervosa. Eating disorders are associated with severe feelings, actions, and attitudes towards food and weight.

6. Impulse Control and Addiction Disorders 

In this list of types of mental disorder, this is used to describe the inability to resist impulses or urges and performing acts that are considered harmful to self or to others. Some examples of impulse control disorders are starting fires (pyromania), stealing (kleptomania), and uncontrollable gambling. In terms of addition disorders, people often become so wrapped up in something that they no longer focus on anything else and they neglect their relationships and responsibilities. Substance use and dependency disorders fall under addiction disorders. These addictions can manifest as impaired social, emotional, physical, educational, and/or vocational functions by the user. The substances that are abused can be either legal substances like alcohol and household cleaners or illegal drugs, like marijuana, opiates, cocaine, and Ecstasy.

7. Personality Disorders

Examples of personality disorders are antisocial personality disorder and paranoid personality disorder. In personality disorders, people's behavioral pattern and thought processes are very different from societal norms, and they are so inflexible that they impair everyday life. They may become so severe that they cause distress to the individual and disrupt their job or school and relationships.

8. Developmental and Cognitive Disorders

Although they are often included in diagnostic manuals of mental disorders, mental retardation and learning disabilities do not meet the criteria for mental disorders since they do not impact a person's mood. Instead they are typified by cognitive problems that include impairments with language or with recognition, and they occur in the absence of brain injuries. Similarly, dementia, involves problems with critical thinking and memory. Alzheimer's disease is a trigger for dementia.

Other Rare Types of Mental Disorders

1. Adjustment Disorders

A diagnosis of adjustment disorder is given if a person develops behavioral or emotional symptoms after experiencing a stressful event. These stressors can be natural disasters (earthquakes or tornadoes), catastrophic events (automobile accidents or a major medical diagnosis), or interpersonal issues (loss of a loved one or a job, a divorce, or a substance abuse problem). For the diagnosis with an adjustment disorder, the symptoms have to start within three months of experiencing the stressor to within six months after the stressor is eliminated.

2. Dissociative Disorders

A person with dissociative disorder suffers with extreme disruptions in consciousness, identity, memory, and perception of self and surroundings. These disorders usually occur after a person experiences a tremendous stress due to some type of trauma or accident. Some common examples of dissociative disorders are depersonalization disorder and dissociative identity disorder (multiple personality disorder or "split personality disorder").

3. Sexual and Gender Disorders

Sexual and gender disorders refers to disorders that impact sexual behaviors, sexual desires, and sexual performance. Examples of these disorders are gender identity disorders, sexual dysfunctions, and paraphilias.

4. Factitious Disorders

Factitious disorders refer to conditions in which a person fakes emotional and/or physical symptoms to garner attention either in the role of patient or as a person needing assistance.

5. Somatoform Disorders

When a person experiences physical manifestations of an illness in the absence of a true medical cause for their symptoms, they meet the criteria for the diagnosis of somatoform disorder. Unlike factitious disorders, people with somatoform disorders are not reporting symptoms to get attention.

6. Tic Disorders

Involuntary vocalizations or body movements that are repetitive, sudden, and quick are referred to as tics. People that display tics are diagnosed with a tic disorder. A classic example of a tic disorder is Tourette's syndrome.