Evolution has made this mental harmonious functioning state the most pleasant and desired state attainable, because knowledge has so much survival value. A diverse set of research findings support some of the main ideas of the harmonious functioning model. There is some evidence of a general motivational and arousal system that controls a range of reactions from mania at one extreme to depression at the other. Moderate states may be consistent with harmonious functioning. Other theories will be discussed next .
Many people think that the word anxiety refers only to intense degrees of anxiety.
However, I am using the term to include nervousness, stress, fear,guilt, and other similar emotional states. Many people confuse the emotion depression with clinical depression. The emotion depression ranges from mild forms such as slight sadness or unhappiness to intense grief or severe depression. Almost every day we all probably feel some degree of depression for at least a short time. Clinical depression is a label used for a psychological disorder-prime features of which include prolonged, intense depression and suicidal thinking.