What you are experiencing may be something called seasonal affective disorder. Seasonal affective disorder is a form of depressive disorder that cycles with the seasons. People with this disorder tend to have episodes of depression
in the darkest winter months, and their moods tend to improve in summer months.
The exact cause of seasonal affective disorder is not entirely known. It is thought that in part it does have something to do with lack of sufficient sunshine, because sunshine is linked both subjectively to better mood and also objectively to changes in some of the brain's chemicals. Other factors may include changes in the body's natural internal clock, or day-night rhythm, associated with imbalance in the body's melatonin levels.
If you feel you have seasonal affective disorder, you should talk to your primary care doctor
or your psychiatrist
. Seasonal affective disorder can be effectively treated. Sometimes, light therapy is a sufficient form of treatment. Other times anti depression medications can be taken, either year round or just for the months surrounding the time in the winter when the symptoms are at their worst. Your doctor can help you decide what the best form of treatment for your case will be.