Answer:
A mood disorder is a mental illness which is caused by a chemical imbalance in the brain. This imbalance causes your moods to swing uncontrollably.
In unipolar depression, you feel very sad for no good reason, and often feel tired, defective, and may even have physical symptoms such as headache or nausea.
In bipolar disorder or manic depression, your mood swings between depression and a feeling of uncontrolled elation known as mania.
In anxiety disorders, you feel anxious, nervous, and worried for no good reason.
All mood disorders respond quite well to proper medication, and often can be cured or brought under total control with a combination of medication and psychological therapy.