Positive Psychology is a (welcome) departure from much of traditional psychology, which has focused to a greater extent on “problems,” on pathology. Traditional psychology could hardly be described as focusing on the positive. With the sudden appearance of the Positive movement, that picture is changing dramatically.
Part of the focus of Positive Psychology is on the positive emotions - joy, satisfaction, gratitude, enthusiasm, and the like. Psychologists have long argued that there is obvious adaptive value in the negative emotions. Fear and anger, for example, can motivate actions that have obvious value in promoting survival. We walk in the woods, see a bear, feel fear, and run, hide, or take other action in an attempt to escape harm. We were challenged as a student with a pop quiz, felt fear and anxiety, and we focused all our efforts on the task at hand.
In short, when we psychologists talk about emotion, we almost always automatically mean negative emotion. Even among non-psychologists, calling someone “emotional”, or having an “emotional” reaction, is usually code for fear, anger, upset, anxiety - one of the negatives.