If the changes in season drop you off into depression, you might have seasonal affective disorder or SAD. SAD usually begins and ends at the same times each year, mostly during late fall or early winter. SAD symptoms include loss of interest, weight gain, low energy, anxiousness, feeling worthless, and the like. Some of the most common ways to combat SAD include getting enough Vitamin D and sunlight, relaxing, eating healthy, and staying on schedule.
Source: https://www.military.com/military-fitness/pushing-through-dark-ages-and-getting-ready-spring