This is a respectful article on SAD, by that I mean it actually respects how severe the illness can be. I copied the main article, but there are other good looking articles on SAD, depression and CBT (I've been reading this Science Daily site for hours), so you might want to check out the link it came from http://www.sciencedaily.com/articles/s/seasonal_affective_disorder.htm
Seasonal affective disorder
Seasonal affective disorder, or SAD, also known as winter depression is an affective, or mood disorder.
Most SAD sufferers experience normal mental health throughout most of the year, but experience depressive symptoms in the winter or summer.
SAD is rare, if existent at all, in the tropics, but is measurably present at latitudes of 30 degrees N (or S) and higher.
Seasonal mood variations are believed to be related mostly to daylight, not temperature.
For this reason, SAD is prevalent even in mid-latitude places with mild winters, such as Seattle and Vancouver.
People who live in the Arctic region are especially susceptible due to the effects of polar nights.
Prolonged periods of overcast weather can also exacerbate SAD.
SAD is a serious disorder, sometimes triggering dysthymia or clinical depression.
A number of treatments exist for SAD.
These include light therapies, medication, ionized-air reception and cognitive therapy..
For more information about the topic Seasonal affective disorder, read the full article at Wikipedia.org, or see the following related articles: