And this year, the rotten summer means that up to 10 million people will experience 'winter blues' and are likely to be feeling gloomy and down during the winter months.
So how can you make yourself feel better and beat the winter blues? We have some top tips and expert advice from psychologist Donna Dawson and consultant to St John's Wort medicine Karma.
1. Try some light therapyThis is always the top treatment option suggested by experts. They think that SAD is caused by a lack of light that cuts serotonin in the brain - this is the chemical in the body that makes you feel happy.
You can buy a small lightbox and spend 30 minutes a day in front of it if you suffer regularly. They can be expensive, but people who've tried them swear by their benefit.
- Read how a lightbox changed Nikki's life
If you can't afford a lightbox, then make sure you get outside more often. Donna Dawson is a psychologist specialising in personality and behaviour and recommends a daily dose of sunlight.
'Don't stay cooped up in your dark, over-heated, poorly-ventilated office or home. Natural sunlight can help to synchronize our body rhythms. Without enough natural light, hormones can become unbalanced and cause mood disturbances, such as low feelings and depression. On sunny, or even cloud-covered days take a walk or eat your lunch on a park bench.'