It’s easy to get the blues in the winter. The gloomy weather, post-holiday food comas, and post-holiday return to routine can really get you down. But most of us continue on with our daily lives, dreaming of warmer days.

For some people though, the winter blues are more than an inconvenience. Seasonal affective disorder (SAD) is a legitimate mental illness where sufferers experience anxiety or depression during a certain season. It may sound too crazy to be true, but it’s a legitimate “course specifier” for major depressive disorder in the DSM-V!

With winter in full swing, it’s the perfect time to learn about SAD.