For many in the northern hemisphere this time of year, the shorter days and longer nights are accompanied by seasonal affective disorder. The acronym is, rather appropriately, SAD.
Many are flattened every year and have no idea what's happening. They're irritable and depressed. They're tired and lethargic, dragging out of bed in the morning.
They may have a hard time concentrating. Their love life can suffer. Cravings for carbohydrate comfort foods may spike for months at a time as the winter weight accumulates.
In severe cases, sufferers of SAD experience thoughts of suicide and intense withdrawal from the rest of the world.
Jo Clarke of Telford, Shropshire, UK has always found winter to be a challenge. After she got hit with Chronic Fatigue Syndrome some years ago, her experience with SAD intensified.
"I start to feel the dread coming down on me round about November time, just after the clocks go back and I celebrate the Winter solstice rather than Christmas, because it is then that the days start getting longer again. But it's a long climb out till I start feeling better round about March time."
Seasonal affective disorder is often misunderstood and misdiagnosed as hypoglycemia, hypothyroidism or mononucleosis. Or paradoxically, it may be seen as not physical at all, and the person struggling with very real symptoms of SAD may be everlastingly told to buck up and pull themselves together, as though this inner drooping is some whim on their part.
But physical factors are all too real in this supposed case of the blues.
As sunlight decreases, so do your levels of melatonin, a chemical involved in your sleep patterns. When it's out of whack, melancholy, lethargy and carbohydrate cravings are common. And vitamin D levels and serotonin plummet in a downward spiral.
Albert Driver of Wilmington, Delaware struggled with seasonal depression for many years without knowing what was wrong. Year after year, as autumn daylight waned, he experienced disturbing changes.