Note that "During snowy winter weeks" it's also the darkest part of the year, which also has a known correlation to (un)happiness. So it may be "just" the ligh

Note that "During snowy winter weeks" it's also the darkest part of the year, which also has a known correlation to (un)happiness. So it may be "just" the light or it could be both your lifestyle change and the lack of light siphoning happiness.