As Kinky Kitten said, sometimes your past can remind you of things that have occured... maybe this time of year has held many bad memories for you that bring up these kinds of feelings. But there is something else that I think should be mentioned and you should look into it. It might apply to you. Some people do suffer from seasonal depression, or seasonal affective disorder. Here's just one link, but if you do a quick online search, you will find several others.
http://www.mayoclinic.com/health/seasonal-affective-disorder/DS00195
I'm sure you've heard of things like the "winter blues"? There's a reason a term like that came around. And since this is around winter time, this situation may apply to you. It's something to consider, and if it applies, you may want to consider talking to a doctor about it. Anything is worth a try, and maybe medication might be right for you (though I could also personally understand if you don't like this option).
Either way, I just thought that was worth putting out there. Understanding can sometimes to wonders in helping a situation. Anyway, I wish I could help more, but those two things are really all that comes to mind.