Mood disorders affect about 10% of the population. Everyone experiences "highs" and "lows" in life, but people with mood disorders experience them with greater intensity and for longer periods of time than most people.

Depression is the most common mood disorder; a person with depression feels "very low." Symptoms may include: feelings of hopelessness, changes in eating patterns, disturbed sleep, constant tiredness, an inability to have fun, and thoughts of death or suicide.

People with manic depression have periods of depression and periods of feeling unusually "high" or elated. The "highs" get out of hand, and the manic person can behave in a reckless manner, sometimes to the point of financial ruin or getting in trouble with the law.