Seasonal Affective Disorder is a medically recognized depressive disorder. The DSM IV (the primary diagnostic manual used by psychiatric clinicians to makes diagnoses) identifies SAD as a subtype of Major Depressive Disorder. It occurs more often in women than men, and has a seasonal component (for a given individual, SAD starts at around the same time each year, and resolves at about the same time of year), and has to occur at least 2 consecutive years in a row. Symptoms can be mild to severe, and treatment can be very effective.

So, to answer your question, SAD is real and it also is a type of depression. You can differentiate between "regular" depression and SAD by looking at the symptom descriptions. The references, below, give complete symptom descriptions. Generally speaking though, symptoms are similiar to hibernating-- think of the Grizzly bear getting ready for winter: irritable, low energy, increased need for sleep, hungry with carbohydrate craving and increased weight, diminished concentration, and decreased libido.

In my several years as a health care practitioner in a northern US location, I have seen excellent responses with appropriate therapy, often without medication. Effective management includes light therapy, Vitamin D (aka, "Liquid Sunshine"), regular exercise, therapy, Omega 3 supplements, and vitamins/minerals. However, if a person is experiencing severe and/or prolonged symptoms, antidepressant medication can be very helpful. See your health practitioner to be fully evaluated, since other conditions can cause SAD symptoms.

If you are interested in taking a circadian rhythm test to see how to best utilize light therapy, go to: http://www.golite.philips.com/