Bipolar disorder is a major mental illness that involves extreme swings in mood, ranging from the low of depression to the high of mania. When depressed, a person may feel sad, have problems with sleeping, eating, and loosing weight, have many negative thoughts about oneself (including thoughts about death and hurting oneself), and experience difficulties with attention and concentration. During periods of mania, the individual may experience euphoric or irritable mood, inflated self-esteem and over-confidence, increased talkativeness, distractibility, and boundless energy, including a decreased need for sleep.