Do you have seasonal affective disorder? How to tell — and what to do about it

Norman Rosenthal moved to the United States from South Africa in 1976, he felt less energetic during the harsh winters. He noticed other people felt the same way. "Just like the autumn leaves, they became depressed on schedule," says Rosenthal.

"In spring, the condition reverses itself." He studied the problem, and published the first research on the syndrome and coined the term seasonal affective disorder, or SAD, in 1984. About 1 in 20 people in the U.S. have SAD, and it typically lasts about 40% of the year, according to the American Psychiatric Association. If you have it, you may feel sluggish or depressed, oversleep, overeat, gain weight and be uninterested in doing things you previously enjoyed.

Many more people have the winter blues, a milder version of SAD, where you feel like a sadder, sleepier or slower version of yourself. With winter just around the corner, here's why you may feel this way — what you can do to feel better. For many people, SAD makes things feel difficult every fall when it gets darker earlier, but better in the bright days of spring and summer, Rosenthal says.

One of Rosenthal's patients described themselves as feeling like a bear in the winter and wanting to hibernate. "So if you feel any identification with a hibernating bear, you might well have SAD," he says. Women are about four times more vulnerable than men, and the condition is more common in the Northern Hemisphere.

While some people don't feel different at all when the seasons change, Rosenthal says others are quite disabled by it. People diagnosed with SAD, he says, are "people who would go to a doctor because the problem was bad enough." Rosenthal says it can be hard to recognize a pattern, because the symptoms creep up on you. "For example, it might be a little bit serious in September and a little worse in October and a little worse in November.

It's a bit like the story of the frog in the bowl that keeps getting warmed up, and he doesn't realize he's going to die because it happens so incrementally." But, he says, recognizing your symptoms and taking them seriously are critical, because SAD can be debilitating or worse. A fundamental part of the physiology of this condition is that some people just need more light. One often recommended fix for this is a SAD lamp.