Depression is a medical illness, an illness with symptoms and a proven course of medical treatment that is effective in more than eighty percent of the cases.

Depression is more than just the occasional bad mood. It is not the natural mourning that takes place after a loss, or the "downs" in life's ordinary cycle of ups-and-downs.

Depression can be difficult to diagnose or to recognize in oneself. The symptoms of depression easily hide behind the ordinary experience of life.

Just a glance at the National Institutes of Health's symptoms of depression checklist reveals that depression overlaps normal, healthy living at many points.

According to the National Institutes of Health, the Symptoms of Depression can Include:

• Persistent sad or "empty" mood
• Loss of pleasure in ordinary activities, including sex
• Decreased energy, fatigue, being "slowed down"
• Sleep disturbances (insomnia, early-morning wakening, or oversleeping)
• Eating disturbances (loss of appetite and weight, or weight gain)
• Feelings of guilt, worthlessness, helplessness
• Thoughts of death or suicide, suicide attempts
• Irritability
• Excessive crying
• Chronic aches and pains that don't respond to treatment

In the Workplace, the Symptoms of Depression Often May Be Recognized by:

• Decreased productivity
• Morale problems
• Lack of cooperation
• Safety problems, accidents
• Absenteeism
• Frequent complaints of being tired all the time
• Complaints of unexplained aches and pains
• Alcohol and drug abuse

Healthy people, of course, regularly experience one or more of these symptoms. At what point, then, do ordinary "downs" become depression?

We must look first at intensity. How intense is the symptom? Hardly noticeable or overwhelming? If any one symptom significantly interferes with friends, family, or work, it can indicate depression.

We must also look at duration. How long have the symptoms been going on? If one has not felt pleasure for an hour, that would not indicate depression. If, on the other hand, one had not felt pleasure for a month, depression (or some other imbalance) may be indicated.

Finally, one must consider the number of symptoms. Many people don't know they have a depression because they experience their symptoms intermittently or at low levels. While none of the symptoms stand out enough to seek medical help, the collective symptoms of depression drain the psyche of the ability to enjoy life.

The National Institutes of Health, therefore, recommends:

A thorough diagnosis is needed if four or more of the symptoms of depression persist for more than two weeks, or are interfering with work or family life.

Because the symptoms of depression are so close to home, and because we human beings are such masters of self-deception and denial, it's difficult to objectively evaluate oneself for depression.