I'm SAD. Not the morose, unhappy emotion that many people feel but SAD, as in Seasonal Affective Disorder.
I have suffered from this problem for as long as I can remember, but it was only 10-12 years ago that I was able to put a name on the feelings, the very real feelings I endure for about six weeks out of every year.
It's more than winter doldrums. It's more than just a case of melancholia, because even when I don't feel especially depressed, I have absolutely no energy to complete the most simple of everyday tasks.