I've felt it myself as I do every Autumn. Christmas seems to be the climax and as soon as that depressing time of the year is out of the way I start to cheer up. In the meantime I try to keep busy, I'm currently in the process of buy a push bike and also trying to work out several bike routes where I'm less likely to get killed. In my 30s I used to cycle 150 miles a week out of necessity, having bought a flat and sold the car because I couldn't have both. The benefit being, so I'm told, that as I'm no stranger to exercise, it shouldn't be difficult now. Reality isn't currently matching theory, but at least with the bike I know I'll enjoy the open air and the countryside (I live on the outskirts of High Wycombe). Sorry, enough about me.
My MIL tells me that the ight box I bought her for Christmas is "marvelous" and trust me, I rarely get praise from the MIL. I feel better on sunny days so lets pray for some good weather over the winter. Take care.