I'm one of those people who have seasonal affective disorder, with the fantastically appropriate acronym: SAD. Below is an article if you want to read more about it. Basically, when the days get shorter, people with SAD feel more sleepy, less social, and they want to eat lots of carbohydrates. They want to hibernate. They are the bear people.
Hibernating is inconvenient in this modern world, and I'm all for flouting mother nature on this one, but let's be real, it's not a disorder, it's a normal reaction to the change in season. You want to hole up, put on some weight for the winter, and sleep more. I could happily spend the winter season in a warm, bright house with my family, and all the food we stored for the winter. I'd read, and listen to Pa play the fiddle. Just don't ask me to go out, and don't ask me to do anything. I think the interesting thing is people in the general population whose pineal glands mistake artificial light for sunlight and don't have that reaction, that's a disorder! But it's a helpful and convenient one.
Exposure to sunlight or a lightbox in the morning helps many people. There is an article in this month's Scientific America about it. I have a light box, but when I moved to a sunnier place I didn't think I'd need it. I'm going to get up at 7 every morning and take a walk, hopefully that will help my body pretend I shouldn't be hibernating. Good luck bear people!
Here's an article about SAD on a buy-your-term-paper website. (Can you imagine writing term papers for your job? Ugh.)
The Center for Environmental Therapeutics has a good questionaire about SAD. I took the quiz and it told me that the best time for me to do light therapy is at 7AM! I don't know how they came to that conclusion, but for years my gut instinct has been that 7AM is my optimal waking up time.
NAMI (The National Alliance on Mental Illness) has a good overview article about SAD.