According to the DSM-IV-TR (p. 356), the two principal or required elements of depression include:interest in life, anhedonia". Likewise, "lack of energy and motivation" is not at all a required symptom of Major Depression.
Often it is accompanied by sleep disorders such as insomnia, including early morning awakening and by feelings of greatly lowered self-worth. Depression is often described as being unable to feel -- even to feel many negative emotions such as sadness. Some depressed individuals will have to sleep or rest all day because their bodies unconsciously know it is best to lay low away from danger during this vulnerable period.
Other symptoms accompanying depression include: changes in appetite, feelings of guilt, failure and worthlessness, thoughts of death, fatigue, and difficulty concentrating, withdrawal, inactivity, slow speech, walking slow, irritability, confusion, crying easily, inability to enjoy things, insecurity, anxiety, sore shoulders and neck, low back pain, low libido, binge eating junk food, inability to show affection, void of emotions, disorganized, hair becomes wiry, eczema, having trouble getting dressed or choosing clothes, feelings of regret for past decisions, inability to function, feeling like no one understands, boredom, fear, desire to be taken care of, paranoia, irrational fears, easily frustrated. Of course, each person will have some of these symptoms, but not all.
Depressions are currently treated, with varying degrees of success, in several ways including: psychotherapy (including cognitive therapy, Psychoanalysis, etc.), antidepressant medication, and electroconvulsive treatment. Some people stop their medication when they feel better, but this is risky since each depressive episode is worse than the previous one. It is as risky as stopping the use of a heart medication when your heart starts feeling better.
Meditation, regular aerobic exercise (30 minutes, 5 times a week), good nutrition, proper sleep hygiene, and avoiding alcohol, caffeine and excessive sugar are extremely helpful in fighting depression. Exploration of one's spirituality has also had an important impact for many people in healing their depression. Writing (or typing) thoughts in a regular journal helps immensely too, as well as getting outside in the sunshine and talking to friends.
Note: The name "Melancholia" (derived from 'black bile', one of the imagined 'humours' of Hippocrates' four humours theory of emotion) appears to be cognate with what is now called depression. It is also the name of an engraving by Albrecht Dürer that allegorically depicts the symptoms of depression.
Psychiatrists have attempted to categorize depression in many ways, one older division was between "reactive" or "exogenous" depressions, which were thought to be depressions caused by other medical condition or an identifiable life trauma or loss; and "endogenous" depressions in which it is difficult to find an external cause. Often depression is repressed anger (in a person who has been oppressed or controlled) or repressed fear (in a person who has been assaulted) and hence episodes of violence and/or major anxiety can alternate with episodes of major depression. Post-traumatic stress disorder, is a form of depression noticed in persons who have been raped, and/or assaulted, in prostitutes, and military personnel and others who have experienced a lot of violence.
Current psychiatric standards do not differentiate between exogenous and endogenous depressions since research appears to show that depressions with similar symptoms have a similar natural history and response to treatment regardless of trigger.
Depressions can also be categorised into being just "unipolar depression" or being a depression that is part of bipolar disorder (also known as "manic depression"), where the patient cycles between a state of depression and a state of mania. It appears to have well-documented physical correlates. Though bipolar disorder often responds well to chemical treatment, it can be harder to treat than clinical depression. This is because the medicines that will bring the bipolar disorder patient up from the deep well of depression can cause him to shift too far into the manic part of the bipolar spectrum and vice versa.
It is theorized that unipolar depression and unipolar mania are the opposite poles of a wider bipolar spectrum.