DEAR DR. GOTT: I am wondering if there is a test for depression. I’m always lethargic and drained, even though I get regular sleep and eat well. I was told by someone that there are two reasons for being tired – too little rest and depression. I get enough sleep but have been incredibly sad for years.

DEAR READER: Your brief inquiry could require far-reaching answers, since there is no single known cause for depression, which can be mild or so severe it heavily affects a person’s ability to function from one day to the next. It is my guess that you have never spoken with a physician about your concerns. If this is the case, you join the vast majority of people who never seek medical treatment.

There are a number of types of depression, including a psychotic form that accompanies delusions, hallucinations or some other form of psychosis. Postpartum depression affects women within a month following delivery. While quite common, it presents for a relatively brief period. Seasonal affective disorder presents in the winter, when there is less natural sunlight. As you might have guessed, SAD remains under control during the balance of the year and can be treated with light therapy. Milder forms of depression aren’t as severe in intensity, and people may not be as disabled as with other types, but they will have an ongoing complaint of not feeling up to par, and they fail to function normally.

The severity, duration and frequency of symptoms will vary. Some people may experience a loss of appetite, a loss of interest in things once pleasurable, become irritable, have insomnia, aches, pains, headache, a feeling of hopelessness and a great deal more.

As can be expected, depression may co-exist with other medical conditions, such as Parkinson’s disease, cancer, diabetes, post-traumatic stress disorder, alcohol or drug abuse, and a family history of depression.

Fatigue can also stem from a number of causes. The first one that comes to mind is iron-deficiency anemia. Then there’s hypoglycemia (low blood sugar), a viral infection, hypotension (low blood pressure), abnormal thyroid function and an immune-system deficiency. You might experience muscle pain, occasional irregular heartbeat, headache, an inability to concentrate, morning stiffness and shortness of breath. If other causes cannot be found, perhaps you are suffering from chronic fatigue syndrome.

The key to diagnosing chronic long-standing fatigue is that the symptoms remain, despite adequate sleep. If we couple this with the mild form of depression I mentioned above, these symptoms outwardly fit your profile to a T.

Having said this, I must strongly recommend that you make an appointment with your physician for a complete examination to include blood work, EKG, chest X-ray and anything else he or she recommends. If no abnormalities exist, and perhaps even if they do, request a referral to a therapist or psychiatrist to determine whether the cause is depression.

To provide related information, I am sending you a copy of my Health Report “Medical Specialists.” Other readers who would like a copy should send a self-addressed, stamped No. 10 envelope and a $2 check or money order to Newsletter, P.O. Box 167, Wickliffe, OH 44092. Be sure to mention the title or print an order form off my Web site at www.AskDrGottMD.com.