Depression is a common mental disorder in which a person has depressed mood, loss of interest or pleasure, reduced energy, feelings of guilt or low self-esteem, sleep or appetite disturbances, and lack of concentration. Depression is often accompanied by anxiety symptoms.

As with other diseases, depression is the result of the interaction of many different genetic, biological and psychosocial factors. There is no single cause that could be implicated in the occurrence of depressive episodes.

Epidemiological studies estimate that about 6% of the general population suffers from clinically established depression. Women suffer twice as often as men and the disorder may occur at any age. Depression according to its mechanism of appearance is divided into Primary and Secondary. Secondary depression occurs in the context of another illness, such as Parkinson's disease, while primary is considered when all the other diseases that depression can experience on their path are excluded. Depending on the severity of the symptoms and how it occurs, depression can be categorized as:

• Dysthymia: It is a form of chronic depression that is moderate in severity, but because it extends over time it creates a feeling of inadequacy in the person. The patient with dysthymia, although he can cope with his daily activities, always feels that something keeps him from feeling well.
• Postpartum depression: It is the depression that develops after birth and during the period of puerperal. This period is considered to be of high risk for developing depression in a woman most likely due to major postpartum and puerperal hormonal changes.
• Psychotic depression: In this type of depression, besides the usual symptoms mentioned, there are hallucinations (e.g. the patient hears voices but there are no people in the environment) and / or delusions (false beliefs that are not based on any real fact, for example the patient is totally convinced that he is guilty of acts he has done in the past and that is why he even deserves to die.) Psychotic depression is always serious and may require hospitalization.
• Major Depression: It is the usual form of severe depression and requires treatment by a psychiatrist.
• Informal depression. Sometimes psychiatrists report a depression that does not show classical symptoms, e.g. the patient may experience overeating and hypersomnia instead of insomnia. Also sometimes it is said that itis a depression that occurs with many physical symptoms rather than psychic.

Depression is a disorder that can be diagnosed and treated effectively. In most cases, the treatment consists of psychological intervention methods such as cognitive behavioral therapy, individual and group psychotherapy in combination or without pharmaceutical treatment as well as phototherapy and repeated transcranial magnetic stimulation (rTMS). In cases of severe depression, especially when there are psychotic symptoms, intention for suicide, symptoms of denial of food, pregnancy and other, electroconvulsive therapy has proved to be the best-performing method.