I'm also sorry to hear you're feeling down. Years ago there was a study done that basically confirms your notion: long shadows and less sun tend to lower most folk's mood.
There are those of us, however, who get invigorated with a chill in the air,
any chance of snow,
the thoughts of family,
special desserts
and holidays
. A brisk walk just adds to the magic.
"It's the most wonderful time of the year..."
Anyway, I'd only suggest that, rather than dwell on it, you embrace it. Smile as you notice the special beauty that emerges when the leaves get out of the way. If there's fresh snow, step out and just listen to the stillness it provides. It's a library full of sounds that are usually drowned out. And enjoy the excuse for another cup of cocoa!