Depression or moping is a state of low mood and aversion to activity. Depressed persons may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable or restless. They may lose interest in activities that once were pleasurable, experience loss of appetite or overeating, or problems concentrating, remembering details or making decisions; and may contemplate or attempt suicide. Insomnia, waking early, excessive sleeping, fatigue, loss of energy, or aches, pains or digestive problems that are resistant to treatment may be present.
The Diagnostic and Statistical Manual of Mental Disorders defines a depressed person as experiencing feelings of sadness, helplessness and hopelessness. In traditional colloquy, "depressed" is often synonymous with "sad", but both clinical depression and non-clinical depression can also refer to a conglomeration of more than one feeling.
While often described as a dysfunction, there are also strong arguments for seeing depression as an adaptive defense mechanism.

There are many symptoms and signs that signify depression. Please note that depression is a serious disorder and one should contact a doctor if these symptoms occur. The frequency, duration, and severity of these symptoms will vary depending on the individual. Some signs and symptoms that can occur include:

• never seem to be enough
• dullness
• chronic sadness never seeming to end
• obsessions
• shakiness when feeling most down
• mood swings
• Persistant sadness, the feeling of being "empty", and anxious
• Changes in sleep patterns (insomnia, in particular during the early hours of the morning, or oversleeping which is also known as hyersomnia)
• Loss of Interest
• Appetite or weight changes (a significant weight gain or loss, by more than 5% of body weight)
• Irritability or Restlessness
• Loss of Energy
• Concentration Problems
• Unexplained aches and pains (An increase in physical complaints like back aches, headaches, or pains in other areas)
• Frequent thoughts of Suicide or Death

• Biological
• Psychological
• Social

Biological causes: I. Chemicals / Neurotransmitters: Neurotransmitters are the chemical messengers, which are critical in the transmission of nerve impulses in our brain and nerves. The level of certain neurotransmitters, NORADRENALINE & SEROTONIN are decreased in the brain. Most of the medications used for treating depression (Anti depressants) help in elevating the levels of these chemicals in the brain.

II. Genetic: Major depression also seems to occur in generation after generation in some families, although not as strongly as in bipolar I or II. Indeed, major depression can also occur in people who have no family history of depression.

III. Hormonal imbalance: Though the exact mechanisms are not understood but imbalance of female sex hormones can lead to depression. Depressions in the postmenopausal and post partum (after delivery) period are the examples.

Psychological causes:

I. Personality/ Attitudes: Following types of personality traits predispose to depressive illness.

• Very ambitious
• Anxious
• Obsessive/perfectionist
• Setting very high standards for self
Persons having above traits/attitudes are more likely to experience depressive episodes in their lives as compared to people who don't have such type of personality.

II. Coping strategies with life events: How we deal with stressful events like separation/divorce/death, etc. determines how predisposed we are to depression. People who are

• Impulsive
• Aggressive
• Self centered
Are more likely to have depression.

Social causes and social supports:

• A lot of stressful life events like death/divorce/disease predispose to depression.
• Interpersonal relationships matter a lot - good relations with the friends / spouse / siblings have a positive effect in preventing depression.
• Single people are more prone to depression than couples.
• Similarly, studies have found divorced persons to be more prone to depression.