Definition:
Mood swings are rapid -- and often extreme -- fluctuations in one's emotional state, involving alternating between feelings of happiness and well-being and feelings of anger, irritability or depression.
Among the possible causes of mood swings are an imbalance in the brain chemicals associated with mood regulation, as in the case of bipolar disorder, and the hormonal changes associated with the menstrual cycle or menopause. In addition, mood swings may occur in men who abuse steroids (often called 'roid rage).
