According to the Mayo Clinic...
"If you have a mood disorder, your general emotional state or mood is distorted or inconsistent with your circumstances."(1) In other words, there may be times when your thoughts are interpreting your situation in a distorted fashion. These distorted thoughts results in distressing emotions and feelings.
You are not alone. The distorted thoughts, and resulting negative emotions of many people, may be as a result of a distressful event in your life or a chemical imbalance in how your brain processes serotonin, norepinephrine or dopamine. You may have also developed ways of interpreting your circumstances that are working against your well being.
Some major examples of emotional distress that may require the help of a therapist include: