Winter is coming, and if you tend to feel sluggish or sad during those dark, dreary days of the season, it could be Seasonal Affective Disorder (SAD) to blame. The symptoms mimic those of regular depression. Shorter days and a lack of sunlight can cause a dramatic dip in serotonin, the body's natural mood stabilizer. Paul Verhaeghen, professor in the School of Psychology, suggests light therapy by using a light box or lamp with 2,500-10,000 lux. Using it one hour a day, preferably first thing in the morning, simulates natural sunlight and can increase energy.