What are mood swings? Mood swings are excessive or abrupt changes in your frame of mind. Your mood may suddenly shift from elation and euphoria to extreme sadness or terror, and then on to another emotion. In some cases, mood changes are reactions to your environment or circumstances, although the intensity of the mood might seem out of proportion with the significance of the event. In other cases, mood swings may occur for no apparent reason. Moods are thought to result from interplay of chemicals in the brain; the cause of mood swings is not known, but they may be related to imbalances in these chemicals. Mood swings can occur as a symptom of psychiatric disorders, such as bipolar disorder or borderline personality disorder, or they may result from a medical condition that directly affects the central nervous system, such as dementia, brain tumors, meningitis, and stroke. Mood swings can also result from conditions that deprive the brain of nutrients and oxygen, such as lung and cardiovascular diseases. Substance abuse, medication side effects, and hormonal changes are other potential causes of mood swings. Academic, employment, financial, legal and relationship problems may result from mood swings. Mood swings can be symptoms of serious, even life-threatening, conditions. Seek immediate medical care (call 911) for seizure; serious injury; or threatening, irrational or suicidal behavior. If your mood swings are persistent, worsen, cause you concern, or lead to academic, employment or relationship problems, seek prompt medical care.