What are the symptoms of depression/ OCD / suicidal depression? How we can identify a person by his behavior?

Question

How to identify a person is suffering from depression/ OCD / suicidal depression? How he behaves and act while he is suffering from above?

Answer 1

The most credible source for diagnosis and evaluation of mental conditions is the Diagnostic and Statistical Manual of Mental Disorders (DSM), which is published and updated every few years by the American Psychiatric Association. The latest and most updated edition is the 5th edition.

Despite being a professional manual and guidelines for psychologists and psychiatrists, the criteria for diagnosis that are listed for each psychiatric condition covered in the book are (mostly) written in a style that laymen can also understand.

Here is a reprint of the diagnostic criteria for Major Depressive Disorder, and here is a reprint of the diagnostic criteria for Obsessive-Compulsive Disorder (OCD).

Please note:

1. Due to the nature of this subject (i.e. wide diversity of presentations), a person does not necessarily have to exhibit all of the signs in order to be diagnosed with a certain mental condition.
   This point may be illustrated by the beginning of the Major Depressive Disorder entry: "Five (or more) of the following symptoms have been present during the same 2-week period and represent a change from previous functioning..."
2. Diagnosis is best left for medical professionals, but there is great benefit in early detection of relevant signs by family members or friends. If you are asking as a non-professional, then read through the criteria and be observant. This may save a life.