What is it?
 

Sadness causes attention to be focused on what is lost.  It takes away energy and forces us to mourn loss and make psychological adjustments necessary for life to continue.
 

How do you fix it?
 

Sadness can be overcome by challenging the thoughts that cause it.  Also, upbeat distractions that are purposely planned are helpful at lifting the mood.  The most effective of these are exercise and accomplishing small goals such as cleaning the house.  Volunteer work is very helpful in lifting sadness, but people rarely do it.
 
 

Medical Effects
 

One aspect of sadness is the feeling of isolation.  Studies over two decades of thirty-seven thousand people have shown that isolation doubles the chances of sickness or death.  Also, in numerous studies of patients with diseases, those who were more depressed were far more likely not to survive than those that were not depressed.  This indicates that curing depression is very important medically, as well as psychologically.

Spoiled hopes, unattainable dreams
lost passion in society's blurring eye
brandishing desires, opinions left to die
feelings rejected, increasing pressure bursting fragile seams.

Pain eclipsing sorrow, loneliness, unavoidable emotional rot
continual inconsideration, irrepressible fatigue
lies powerfully thought out, rampant failure in every league
clandestine pleas beneath the surface, impossible to spot.

Deteriorating rationalization, indistinguishable worth
tormented, frightened, far from pleasant
darkness, coldness lingering, cast aside like a peasant
wondering, searching for an identity, lost since birth.

Struggling to forget unspeakable pain
hollow senses, unbelievable emptiness never to be filled
courage forgotten, compassion lost, savagely killed
surrendering life, as tears wash away in the rain.
                                -Unknown

http://members.aol.com/depress/index.htm
                    -Wing of Madness: A depression guide.

http://www.gn.apc.org/da/
                    -The Depression Allience.

http://www.psycom.net/depression.central.html
                    -Dr. Ivan's Depression Central.

http://www.tcnj.edu/~ellisles/BipolarPlanet/
                    -Page dealing with Manic Depression.

http://www.depression.org/
                    -National Foundation for Depressive Illness.