A mood disorder is the reason behind U.S. Rep Jesse Jackson Jr.'s medical leave of absence, according to news reports.
The Democratic Congressman from Illinois, 47, is "receiving intensive medical treatment at a residential treatment facility for a mood disorder," according to a statement, as reported by the Associated Press. "He is responding positively to treatment and is expected to make a full recovery."
There is no word yet on what kind of mood disorder Jackson has.
Nearly 21 million adults -- about 9.5 percent -- in the U.S. have a mood disorder in any given year, according to the National Institutes of Health. For most people, the age of onset is around 30.
The term "mood disorder" is generally used to describe depression and bipolar disorders. Mood disorders occur when brain chemicals are imbalanced, which can be contributed to by major negative life events, according to Ohio State University.
Major depression is one of the most common kinds of mood disorders, and symptoms include overwhelming feelings of sadness, tiredness, distractedness, problems with thinking or making decisions, changes in eating habits, lower sex drive, a decreased interest in doing normal things, irritability and feeling worthless or guilty, according to the Mayo Clinic. If untreated, the depression can lead to relationship problems, anxiety, alcohol or substance abuse, ideas of suicide and anxiety.
Bipolar disorder is another common kind of mood disorder, and occurs when people fluctuate from feeling depressed to feeling manic, according to the Mayo Clinic.
Other common mood disorders include dysthymia (which is having a low, depressed mood for a year or more), substance-induced mood disorder (depression as a result of a substance like drugs or toxins) and mood disorder from a general medical condition (where a medical condition is the cause of the depressive symptoms), according to Ohio State University.
Treatments for mood disorders depend on the person, kind of disorder and the severity of the disorder, but generally include taking antidepressants, undergoing psychotherapy and/or undergoing family therapy, Ohio State University reported.
The Washington Post reported that these days, if a person is hospitalized because of a mood disorder, it's typically to get started on a drug treatment plan.