There is a good test in the book of Asya Kazantseva, you can see it here 7ya.ru
It will just help you and your friend understand whether he is just in a melancholic mood
or you need contact a specialist.
Typical depression is characterized by a triad of symptoms - decreased mood, inhibited thinking and decreased physical activity.
Low mood (hypothymia in medical terms) in depression must be distinguished from the usual blues. With depression, the mood is lowered in the morning and the former joys no longer bring any pleasure. Anhedonia develops - a condition in which a person is unable to receive pleasure, and its more particular variant is anorgasmia, when a person is deprived of the opportunity to receive sexual pleasure, and sexual intercourse is perceived as a burdensome, senseless duty.
Somatic, bodily functions also develop. symptoms. A person noticeably loses weight, loses his appetite, or, on the contrary, begins to consume food in unlimited quantities, especially sweets.
The speech of a patient with depression is sluggish, little emotional, answers questions in monosyllables, reluctantly.
the world begins to be seen by a person in black colors. The past appears to be a series of mistakes, while the future looks hopeless and devoid of any possibility of happiness. At the same time, the patient is accompanied by a deep and irrational feeling of guilt and all this can end very sadly if a person comes to the conclusion that it is better for him to commit suicide than to defile the face of the earth with his presence. Suicide in such a situation is not of a demonstrative nature, a person really has death as his goal.
What I have described is a classic, bookish version of depression. It should be remembered that there are other forms of depression, so it is best to entrust the diagnosis of this disease to a specialist.
If you are concerned about your friend's condition, the best thing you can do as a layman is to be a good friend and a reasonable person ... Talk to him, explain that you are concerned about his condition and want to help him.
If your friend's condition is really serious and depressive symptoms are present, then the best option for help is to find a good psychotherapist (mind you, not a psychologist or psychiatrist). At the same time, you should not be afraid of electric shock and terrible antidepressants that turn a person into a vegetable. Psychopharmacotherapy has taken a big step forward and modern antidepressants do not have such monstrous side effects as it is commonly thought. In addition, pills often play the role of only an adjuvant in treatment, when psychotherapeutic techniques take the main place.