Depression

Depression can be a psychological and/or a psychiatric condition, depending on its root causes. It is common and treatable, but it can come in a variety of forms and levels of severity. 

Psychotherapy benefits many patients suffering from depression. In some cases, anti-depressants may be required to control a chemical imbalance.

There can be relapses of depression in times of stress, so it is important to have a support system. 

Resources: 
Depression by Harvard Medical School
Depression by the National Institute of Mental Health
Depression by John M. Grohl, Psy.D. 
Men and Depression by the National Institute of Mental Health