Clinical depression is a serious and common disorder of mood that is pervasive, intense and attacks the mind and body at the same time. Current theories indicate that clinical depression may be associated with an imbalance of chemicals in the brain that carry communications between nerve cells that control mood and other bodily systems. Other factors may also come into play, such as negative life experiences such as stress or loss, medication, other medical illnesses, and certain personality traits and genetic factors.
Being clinically depressed is very different from the down type of feeling that all people experience from time to time. Depression is not considered a "blue" mood or a personal weakness - not at all the passing sadness that everyone experiences now and then. Occasional feelings of sadness are a normal part of life, and it is unfortunate that such feelings are often colloquially referred to as 'depression.' Clinical depression is a persistent "down" or "empty" feeling that doesn't improve over a normal period of time.
Major depression is manifested by a combination of symptoms that interfere with the ability to work, sleep, and eat; and enjoy once-pleasurable activities. These disabling episodes of depression can occur once, twice, or several times in a lifetime. It is an illness that affects both mind and body and it's a common problem that can occur at any age. At times everyone feels "down" or "sad". These mood changes are usually temporary. However, when a depressed mood persists for one or more months, and interferes with everyday living, it is likely a sign of serious depression that requires treatment. Major depression is the most common type of depression and is characterized by at least five of the major symptoms of depression.
Another type of depressive disorder is manic-depressive illness, also called bipolar depression. Not nearly as prevalent as other forms of depressive disorders, manic depressive illness involves cycles of depression and elation or mania. Sometimes the mood switches are dramatic and rapid, but most often they are gradual. When in the depressed cycle, the illness can have any or all of the symptoms of a depressive disorder. When in the manic cycle, any or all of the symptoms (listed later under mania) may be experienced. Mania often affects thinking, judgment, and social behavior in ways that cause serious problems and embarrassment. For example, unwise business or financial decisions may be made while in a manic phase. Bipolar depression is the depressive phase of manic-depressive illness, in which there are both extreme highs and extreme lows. Bipolar depression symptoms are similar to those of major depression, with certain variations such as excessive sleep and increase in appetite.
A less severe type of depression, dysthymia involves long-term, chronic symptoms that do not disable, but keep a person from functioning at 'full steam' or from feeling good. Sometimes people with dysthymia also experience major depressive episodes. Dysthymia is a milder form of depression that lasts two years or more. It is the second most common type of depression but because people with dysthymia may only have two or three symptoms, may be overlooked and go undiagnosed and untreated.
Seasonal Affective Disorder is a type of depression that follows seasonal rhythms, with symptoms occurring in the winter months and diminishing in spring and summer. Current research indicates that the absence of sunlight triggers a biochemical reaction that may cause symptoms such as loss of energy, decreased activity, sadness, excessive eating and sleeping.