Depression is one of the most common mental health problems, and is characterized by feelings of sadness or despair that last for at least two weeks and often impair a person's ability to carry out their normal responsibilities in life. Dysthymia resembles depression but has a longer duration. Bipolar disorder is characterized by alternating cycles of lows (depression) and highs (mania or hypomania). Cyclothymia is marked by cycles of low-level depression and hypomania (which is typically shorter in length and less severe than mania).