I don't know, where you are from. I grew up in Central Europe.
During winter here, you leave your home while it's dark outside.
When commuting home again, it's already dark also.
It's known that this can cause something we like to call "winter depression".
Looking it up on Wikipedia I've learned the medical term seem to be
"Seasonal affected disorder". I want to share my stake on it.

Symptoms

Seasonal affected disorder can show different symptoms for different
persons.

Seasonal affective disorder (SAD) is a mood disorder subset
in which people who have normal mental health throughout most of the years
exhibit depressive symptoms at the same time each year,
most commonly in the winter.
Common symptoms include sleeping too much, having little to no energy,
and overeating.

Personally I can observe things like a certain apathy. I don't feel hungry most
of the times.

Fighting the symptoms

I'm sure, there are different strategies to combat
SAD.
Personally, I need a strong social web (my family) and a strict time schedule:
I mainly eat because my watch tells me it is about time. It helps me if I
committed to join colleagues on going out for lunch.
Regarding apathy I step down my schedule and focus on what I think yields the
highest return on investment. In other words, I leave more things undone.

For example, I planned to finish up a project I started recently. But got stuck
shortly at end of November. At least I can see where I need to pick my work up
because I wrote them down as GitHub issues.

Another thing I planned for quite some time: Book my train and a place to sleep
for FOSDEM
next year. I should really get this done soon or otherwise the price will go
up more and more.

It's kind of a pity, that you can't work outside during this season.
not because it is cold, but because your laptop will love the rain or snow.
Inhouse sitting close to the window doesn't do the trick either, because the
luminescence isn't good enough to work without electric light.

Any tips?

Are you affected by SAD as
well? If so, what are you strategies to deal with it? I'd like to read your
blog post about it.

Have you heard of selfcare.tech?
It's a website, where developers share links to ressources which help with
coping with mental disorders.