Depression, also known as clinical depression, unipolar depression, major depressive disorder or dysthymic disorder is one of the most common and serious mental health problems affecting millions of people every day.

Depression is characterized by feeling of sadness, gloominess, despair or melancholia that can serious affect patient's regular activities. This condition can last for few weeks to several years (if not treated).

Depression affects women more commonly then man. It usually starts after the age of 15, and those who have genetic predispositions are more likely do develop depression. Also chances of developing depression are increased in married women, adolescents, people living in poverty, unmarried man and women after pregnancy (Postpartum depression).

There are many possible causes of clinical depression and they are usually connected to every day problems such as job loss, financial problems, loss of dear person usually family member, problems with relationship usually in adolescents or young adults, chronic painful diseases, problems with weight (most commonly including obesity), sexual problems, not having enough sleep...
Depression can also originate from negative experiences in the past such as sexual abuse, rape, school problems, being abandoned by dear person, loss of parents...
Although less commonly depression may be caused by certain illnesses such as cardiovascular disease, mononucleosis, hypothyroidism, hepatitis, multiple sclerosis, Parkinson disease. Also certain drugs can trigger depression, most commonly including hormonal contraception and steroids abuse.

Serious depression can sometimes be cause of attempting or committing suicide.

Symptoms of depression include many conditions similar to normal reaction to negative events so making wrong diagnose is very common. Those conditions may include psychological and physical problems.

Psychological symptoms:
- sadness
- frequent crying
- constant negative thinking
- gloominess
- despair
- fears
- nightmares
- incapability of enjoying
- feeling of being worthless and/or guilt
- being worried or anxious
- learning problems
- aggression
- thinking about death and suicide
- increased irritability and intolerance to other people, usually family members
- easy frustration
- loss of interest for many activities patient used to do before (eating, exercise, spending time with friends and family, sex)
- loss of motivation
- slow thinking and frequent confusing
- problems about making decisions
- liability to drugs, alcohol and smoking
- psychotic symptoms (usually hallucinations or delusions)

Physical symptoms:
- loss of energy due to inactivity (sometimes followed by muscle atrophy)
- changes in weight (usually resulting in obesity or anorexia)
- sleep disorders
- not paying attention to hygiene
- speaking problems
- slower movements
- impotents
- feeling of aches and pain without any reason
- menstrual cycle changes
- constipation
- sensitivity to noise
- physical aggression

According to symptoms and seriousness there are 5 main types of depression:

Major depression - severe depressed condition lasting usually for few weeks. Very hard type of depression oftenly provoked by some unpleasant event. Patients are sometimes liable of committing suicide during this period (in about 15% of cases).

Psychotic depression - a depressed mood including psychosis symptoms. This condition usually include psychotic symptoms such as hallucinations or delusions. Also physical aggression is sometime present so patients are more likely to be hospitalized.

Dysthymia - also known as dysthymic disorder is less serious depressed mood lasting for a long time (sometimes for many years) characterized by lack of enjoyment in life. Although less severe it can disable patient's daily activities and provoke sleeping disorders.

Depression and anxiety - includes symptoms of depression mixed with anxienty. Anxienty is unpleasant condition including emotions such as worry, apprehension and fear. There are also physical symptoms that may follow anxienty including heart palpitations, chest pain, headache, nausea and shortness of breath.

Bipolar disorder - also known as Bipolar Affective Disorder or Manic-depressive Illness is a psychiatric condition characterized by episodes of feeling low (depressed) and high (manic). Manic episodes of bipolar disorder may include: excess of energy, usually good euphoric mood, sleep disorders, beliefs in fake powers and abilities, bad judgment abilities, aggressive behavior, poor concentration.