Anger. Where does anger come from? It is a deep, extremely strong, consuming emotion.
Anger can be triggered by anything. You spill your coffee on yourself in the morning. Your friend betrays you. Something very important to you breaks unexpectedly. Although the sources vary, each of these result in similar physical reactions. It’s a pretty consistent feeling, and requires action on the feeler’s part to let the anger go.
Anger tends to root itself deeply in your mind that is separate from rational thought. In order to properly address the emotion, you must trace the true source of the it. Anger is very good at masking its sources in different ways. The reason you tell others you’re angry may/most likely vary from what you truly feel.
Check out the American Psychological Association’s page on anger management: http://www.apa.org/topics/anger/control.aspx