(edited for improved sound: noise and stereo issues, and miscellaneous parts taken out)
Stanford Professor Robert Sapolsky, posits that depression is the most damaging disease that you can experience. Right now it is the number four cause of disability in the US and it is becoming more common. Sapolsky states that depression is as real of a biological disease as is diabetes.
Stanford University:
http://www.stanford.edu/
Stanford University Channel on YouTube:
http://www.youtube.com/stanford