Bipolar disorder (BD), previously known as manic depression, is a mental disorder characterized by periods of depression and periods of abnormally elevated mood that each last from days to weeks, and in some cases months. If the elevated mood is severe or associated with psychosis, it is called mania; if it is less severe and does not significantly affect functioning, it is called hypomania. During mania, an individual behaves or feels abnormally energetic, happy, or irritable, and they often make impulsive decisions with little regard for the consequences. There is usually, but not always, a reduced need for sleep during manic phases. During periods of depression, the individual may experience crying, have a negative outlook on life, and demonstrate poor eye contact with others. The risk of suicide is high. Over a period of 20 years, 6% of those with bipolar disorder died by suicide, with about one-third attempting suicide in their lifetime. Among those with the disorder, 40–50% overall and 78% of adolescents engaged in self-harm. Other mental health issues, such as anxiety disorders and substance use disorders, are commonly associated with bipolar disorder. The global prevalence of bipolar disorder is estimated to be between 1–5% of the world's population.