Like many people, you may develop cabin fever during the winter months. Or you may find yourself eating more or sleeping more when the temperature drops and darkness falls earlier. While those are common and normal reactions to the changing seasons, people with seasonal affective disorder (SAD) experience a much more serious reaction when summer shifts to fall and on to winter.

With seasonal affective disorder, fall's short days and long nights may trigger feelings of depression, lethargy, fatigue and other problems. Don't brush this off as simply a case of the "winter blues" that you have to tough out on your own.

Seasonal affective disorder is a type of depression, and it can severely impair your daily life. That said, treatment — which may include light box therapy — can help you successfully manage seasonal affective disorder. You don't have to dread the dawning of each fall or winter.

Seasonal affective disorder is a cyclic, seasonal condition. This means that signs and symptoms usually come back and go away at the same times every year. Usually, seasonal affective disorder symptoms appear during late fall or early winter and go away during the warmer, sunnier days of spring and summer. But some people have the opposite pattern, developing seasonal affective disorder with the onset of spring or summer. In either case, problems may start out mild and become more severe as the season progresses.

Fall and winter SAD (winter depression)
Symptoms of winter-onset seasonal affective disorder include:

• Depression
• Hopelessness
• Anxiety
• Loss of energy
• Social withdrawal
• Oversleeping
• Loss of interest in activities you once enjoyed
• Appetite changes, especially a craving for foods high in carbohydrates
• Weight gain
• Difficulty concentrating and processing information

Spring and summer SAD (summer depression)
Symptoms of summer-onset seasonal affective disorder include:

• Anxiety
• Insomnia
• Irritability
• Agitation
• Weight loss
• Poor appetite
• Increased sex drive

Reverse SAD
In rare cases, people with seasonal affective disorder don't have depression-like symptoms. Instead, they have symptoms of mania or hypomania, a less intense form of mania, during the summer. This is sometimes called reverse SAD.

Symptoms of reverse SAD include:

• Persistently elevated mood
• Increased social activity
• Hyperactivity
• Unbridled enthusiasm out of proportion to the situation

The specific cause of seasonal affective disorder remains unknown. It's likely, as with many mental health conditions, that genetics, age and perhaps most importantly, your body's natural chemical makeup all play a role in developing seasonal affective disorder.

Specifically, the culprits may include:

• Your circadian rhythm. Some researchers suspect that the reduced level of sunlight in fall and winter may disrupt the circadian rhythm in certain people. The circadian rhythm is a physiological process that helps regulate your body's internal clock — letting you know when to sleep or wake. Disruption of this natural body clock may cause depression.
• Melatonin. Some researchers theorize that seasonal affective disorder may be tied to melatonin, a sleep-related hormone that, in turn, has been linked to depression. The body's production of melatonin usually increases during the long nights of winter.
• Serotonin. Still other research suggests that a lack of serotonin, a natural brain chemical (neurotransmitter) that affects mood, may play a role. Reduced sunlight can cause a drop in serotonin, perhaps leading to depression.

Although seasonal affective disorder commonly begins in young adulthood, it's uncommon in people younger than 20. Some studies show that it's diagnosed more often in women, but that men may have more severe symptoms.

Data about how common seasonal affective disorder is and who is most likely to develop the condition are lacking. Some evidence shows that factors that may increase the risk of developing seasonal affective disorder include:

• Northern locations. Some evidence suggests that seasonal affective disorder is more common among people who live in higher latitudes — or farther from the equator.
• Family history. Some studies have shown that people with SAD are more likely to have family members with the condition. But research about a potential genetic component has been mixed.

Most people experience some days when they feel down. But if you feel down for days at a time and you can't seem to get motivated to do activities you normally enjoy, see your doctor. This is particularly important if you notice that your sleep patterns and appetite have changed — and certainly if you feel hopeless, think about suicide, or find yourself turning to alcohol for comfort or relaxation.

Seasonal affective disorder isn't recognized by psychiatric professionals as an official, distinct disorder. However, it can be diagnosed as a subtype of depression or bipolar disorder.

To help diagnose seasonal affective disorder, mental health providers perform a thorough psychological evaluation. They ask many questions about your mood, seasonal changes in your thoughts and behavior, your lifestyle and social situation, and sleeping and eating patterns, for example. You may also fill out psychological questionnaires. And you may have a physical exam to check for any other health problems that may be causing or contributing to depression symptoms or manic symptoms.

Even with a thorough evaluation, it can sometimes be difficult for your doctor or mental health provider to diagnose seasonal affective disorder because other types of depression or mental health conditions may mimic SAD. Diagnosing seasonal affective disorder depends on whether:

• You've experienced depression and other symptoms for at least two consecutive years, during the same season
• The periods of depression have been followed by periods without depression
• There are no other explanations for the changes in your mood or behavior

Take seasonal affective disorder seriously. Like its cousin depression, seasonal affective disorder can have serious complications if left untreated. These complications may include:

• Suicidal thoughts or behavior
• Social withdrawal
• School or work problems
• Substance abuse

Like depression, it's often possible to successfully manage seasonal affective disorder. In milder cases, you may be able to take measures on your own, such as spending more time outdoors or sitting closer to bright windows while at home or in the office.

Other treatments for seasonal affective disorder include:

Light therapy
Because increased sunlight improves symptoms, light therapy is often a main treatment for many people with seasonal affective disorder. However, light therapy hasn't been officially approved as a treatment by the Food and Drug Administration because of a lack of definitive evidence about its effectiveness in clinical trials. Before you purchase a light therapy box or consider light therapy, consult your doctor or mental health provider to make sure it's right for you.

Light therapy mimics outdoor light and causes a biochemical change in your brain that lifts your mood, relieving symptoms of seasonal affective disorder. In light therapy, you sit a few feet from a specialized light therapy box so that you're exposed to very bright light. Light therapy is generally easy to use and has relatively few side effects.

Medications
Some people with seasonal affective disorder benefit from treatment with antidepressants or other psychiatric medications, especially if symptoms are severe. The Food and Drug Administration has approved bupropion extended release tablets (Wellbutrin XL) for the prevention of depressive episodes in people with a history of seasonal affective disorder. Other antidepressants commonly used to treat seasonal affective disorder include paroxetine (Paxil), sertraline (Zoloft), fluoxetine (Prozac, Sarafem) and venlafaxine (Effexor).

Your doctor may recommend starting treatment with an antidepressant before your symptoms typically begin each year. He or she may also recommend that you continue to take antidepressant medication beyond the time your symptoms normally go away. This strategy can help prevent worsening of symptoms.

Keep in mind that it may take several weeks to notice full benefits from an antidepressant. In addition, you may have to try several different medications before you find one that works well and has the fewest side effects. Like other medications, all antidepressants pose the risk of side effects and some have health precautions that you and your doctor must discuss.

Psychotherapy
Psychotherapy is another option to treat seasonal affective disorder. Although seasonal affective disorder is thought to be related to biochemical processes, your mood and behavior also can contribute to symptoms. Psychotherapy can help you identify and change negative thoughts and behaviors that may be making you feel worse. You can also learn healthy ways to cope with seasonal affective disorder and manage stress.

There's no known way to prevent the development of seasonal affective disorder. However, if you take steps early on to manage symptoms, you may be able to prevent them from getting worse over time. Some people find it helpful to start treatment before symptoms would normally start in the fall or winter, and then continue treatment past the time symptoms would normally go away. If you can get control of your symptoms before they begin, you may be able to head off serious changes in mood, appetite and behavior that can disrupt your daily life.

You can take action to help cope with seasonal affective disorder. Here are tips to help you manage the condition, in conjunction with your doctor or mental health provider:

• Stick to your treatment plan. Take medications as directed and attend therapy appointments as scheduled.
• Let there be light. Make your home sunnier and brighter. Open blinds, add skylights and trim tree branches that block sunlight.
• Get out. Get outdoors on sunny days, even during winter. Take a long walk, eat lunch at a nearby park, or simply sit peacefully on a bench and soak up the sun.
• Exercise regularly. Physical exercise helps relieve stress and anxiety, both of which can increase SAD symptoms. Being more fit can make you feel better about yourself, too, which can lift your mood.
• Take care of yourself. Get enough rest, eat a balanced diet and take time to relax. Don't turn to alcohol or unprescribed drugs for relief.
• Practice stress management. Learn how to better manage stress. Unmanaged stress can lead to depression, overeating, or other unhealthy thoughts and behaviors.
• Socialize. Stay connected with people you enjoy being around. They can offer support, a shoulder to cry on or a joke to give you a little boost.
• Take a trip. If possible, take winter vacations in sunny, warm locations if you have winter SAD, or cooler locations if you have summer SAD.