this information was used directly from www.depression.com my comments are all in this color.

Normal Depressed Mood & Grief

These conditions are natural reactions to losses in life. They typically involve sadness, lethargy, and in serious cases -- for example, grief after the death of a loved one -- often despair, anger, insomnia, poor appetite, or weight gain, obsessive thoughts about the lost person, and terrible guilt about any problems in the depressed person's relationship with the deceased individual. What makes these reactions normal is that people eventually recover. After losing a ball game, it may take a day or two to bounce back. After a layoff, it may take a few months. After the death of a loved one, it may take up to a year. If symptoms persist, they have a clinical depression and should call a doctor. Normal depressed mood and grief presume a triggering life event. If you or anyone you know displays these symptoms without a loss, or if the depression seems out of proportion to the loss -- such as not getting a raise and sobbing inconsolably for days -- call a doctor.

Adjustment Disorder with Depressed Mood

Life is full of changes. Coping with them can be difficult. Many people feel overwhelmed and "crazy" for a while. Then they get things under control. If they don't, and they become persistently gloomy, angry, and unable to cope, it's most likely adjustment disorder with depressed mood. Adjustment disorder with depressed mood presumes a triggering life event -- the change you have to adjust to. If you or anyone you know displays these symptoms without a life change, or if the depression seems out of proportion to the change -- such as moving to a new city and not being able to get out of bed -- call a doctor.

Mild Depression (Dysthymia)

Dysthymia (pronounced dis-THIM-ee-uh) involves chronic depressed mood, poor self-esteem, and low-level symptoms of major depression (see below). "People with mild depression can still function, but they're sad sacks," says San Francisco psychiatrist Michael Freeman, M.D. "They consider themselves losers." (I object here.) Dysthymia may or may not have a triggering life event. Quite often, there is nothing to blame it on -- no loss or life change. This can be confusing for both the person affected, and their loved ones. But just as you can catch a cold seemingly out of nowhere, you can also slip into dysthymia for no apparent reason.

Major Depression

When people say "seriously depressed," this is what they mean. Major depression often causes despair and hopelessness so profound that the person loses interest in life, becomes incapable of feeling pleasure and sexual arousal, and may be unable to get out of bed or eat for days at a time. But this illness may also cause other symptoms not easily recognized as depression: weight loss or gain; anxiety, irritability, or agitation; chronic indecisiveness; or sleep disturbances (insomnia or sleeping all the time). In other words, you can suffer a major depression and not feel blue. Very often, major depression strikes without any triggering loss. This can be confusing and frustrating for both the person affected, and their loved ones. We want our illnesses to have clear causes. But many serious diseases do not: diabetes, cancer, arthritis. That's how it is with major depression. It's a serious disease that often develops with no discernible triggering event. Officially, according to DSM-IV, major depression involves at least two weeks of deep despair and at least four of the following:

•Sleep problems. Insomnia or sleeping all the time.

• Appetite problems. Loss of appetite or major weight gain.

• Lack of energy. Apathy, lethargy, no interest in anything.

• Feelings of worthlessness, hopelessness, and/or terrible guilt.

• Difficulty concentrating, or unusual indecisiveness.

• Suicidal thoughts, or suicide attempts.

Beyond the almost unbearable misery it causes, the big risk in major depression is suicide. Within five years of suffering a major depression, an estimated 25% of sufferers try to kill themselves. The myth is that people who talk about suicide don't attempt it. The fact is that many people announce their intention before their suicide attempts. Take any talk of suicide very seriously, and make sure the person gets professional help. Call their doctor immediately, if possible.

Bipolar Disorder (Manic-Depression)

About 1% of the American population experiences bipolar disorder annually. This illness involves major depressive episodes alternating with high-energy periods of wildly unrealistic activity. A manic friend might, for example, call at 3 a.m. to announce in all seriousness that she's flying to Hollywood immediately to marry Robert Redford, and star in his next movie. Typically, bipolar disorder develops without any clear cause.

Atypical Depression

"Atypical" means unusual. Instead of feeling unrelenting gloominess and lethargy, a person with this condition might seem deeply depressed for a few days, then fine for a while, or anxious and irritable. Like many other forms of depression, the atypical variety often develops without a triggering event.

Seasonal Affective Disorder (SAD)

This condition is often called "winter blues." A reaction to lack of sunlight in winter, mild or major depression develops in late fall and clears up in early spring. As distance from the equator increases, this condition becomes more common. In the northern hemisphere, December, January, and February are the worst months. (this seems a little unlikely)

Postpartum Depression

New mothers typically expect to feel overjoyed after giving birth. But because of the enormous hormonal changes of delivery and the challenges of dealing with an infant, some two-thirds of women feel transient sadness. About 10% to 15% become clinically depressed. And about one in 1000 become so severely depressed that they must be hospitalized for their own safety and the safety of their baby.

The various types of depression don't have clear boundaries. It takes professional judgment to know when normal grief or an adjustment disorder cross the line to become the more serious forms of depression. Friends, relatives, and family doctors often miss the subtle signs that point to a need for professional help, a big reason why clinical depression often goes undiagnosed and untreated, and why so many people attempt suicide.