Having moved from CA to the NE ten years ago I can tell you they are real! Although I do wonder if part of it is doing less activity - as I'm much less inclined to be outside in the cold weather.

After several years my fix has been to make sure I get out and at least walk a little every day, and stop eating sugar if I can help it! :-) I'm convinced that the moods that sugar bring, along with the inactivity and darkness all contribute to borderline depression for me.