Everyone has days when they feel down for no reason or just can't get motivated on a cold winter morning. But if you find yourself experiencing drastic mood changes every year when fall and winter roll around, you may have Seasonal Affective Disorder. Seasonal Affective Disorder, called "SAD," is a type of recurring depression that coincides with seasonal variations. It commonly occurs during late fall and continues through winter, occurring less commonly in spring and summer. And the ensuing depression typically increases in severity as the season progresses. At least a half million people in the U.S.A. are affected by SAD between September and April every year. It's also believed that a milder form of SAD, referred to as the "Winter Blues" affects even more people. SAD is most common in areas where winter days are the shortest. It can affect people of all ages, but typically occurs most commonly between the ages of 15 and 55, with women accounting for three out of every four sufferers. Symptoms of SAD may include feeling moody, grumpy, anxious or unhappy. Sufferers also tend to sleep more, lack energy and crave carbohydrates. Typical depression symptoms such as lack of interest in normal activities, social withdrawal and decreased sexual interest may be present as well. People who have SAD symptoms in the spring and summer often experience insomnia, lack of appetite, weight loss, crying spells and decreased concentration. The precise cause of SAD is unknown. However, experts have identified several factors that are likely contributors. For example, reduced sunlight during the winter months is believed to disrupt the body's circadian rhythm or "biological clock," which can lead to feelings of disorder and depression. Decreased sunlight may also cause a drop in the brain chemical serotonin; a neurotransmitter that helps regulates mood and emotions. Seasonal changes may also result in a disruption of the body's natural levels of melatonin, a sleep-related hormone that the body produces in increased amounts in darkness. High levels of melatonin are associated with depression symptoms. Also, as with other types of depressive illnesses, people with a family history of the disorder are more likely to be affected by SAD. The level of depression associated with SAD is typically mild to moderate. In some cases, however, the depression can be severe enough to interfere with daily living. So it's important to consult a mental health professional for an accurate diagnosis. Diagnosing SAD involves meeting criteria stated by the American Psychiatric Association in the DSM IV manual including the presence of depression and other symptoms for at least two consecutive years, during the same seasons every year, followed by periods without depression when the seasons change. The most common treatment for SAD is bright light therapy using a light box that simulates natural light. This is thought to suppress melatonin production and help restore the body's natural circadian rhythms, with symptoms often relieved within a week. People who experience SAD during the spring and summer months may find relief by traveling to a cooler climate. When symptoms interfere with normal activities, SAD may also be treated with medication. Typically antidepressants from the serotonin selective reuptake inhibitor family such as Prozac, Zoloft, Paxil, Celexa and the antidepressant Wellbutrin is specifically FDA approved for SAD. Counseling or behavioral therapy can also be effective in helping SAD sufferers manage symptoms. Other ways to manage SAD symptoms include exercising regularly, maintaining healthy eating and spending more time outside. Untreated, SAD may worsen and lead to: substance abuse; problems with school, work or relationships; and suicidal thoughts or behaviors. If you, or someone you know, may be suffering from SAD, please consult a mental health professional.