Rep. Jesse Jackson Jr. being treated for bipolar disorder at Mayo Clinic

Rep. Jesse Jackson Jr. (D-Ill.) is being treated for bipolar disorder at the Minnesota-based Mayo Clinic, the facility revealed Monday in a statement.

The clinic said Jackson "is responding well to the treatment and regaining his strength," but declined to say when — or if — the nine-term Democrat would return to Capitol Hill.

"Bipolar II disorder is a treatable condition that affects parts of the brain controlling emotion, thought and drive and is most likely caused by a complex set of genetic and environmental factors," Mayo's statement reads. "Congressman Jackson underwent gastric bypass surgery in 2004. This type of surgery is increasingly common in the U.S. and can change how the body absorbs food, liquids, vitamins, nutrients and medications.

"No time frame is specified for another update on Congressman Jackson's condition," the clinic added.

Questions about the condition and whereabouts of Jackson have been swirling around Washington and Chicago since mid-June, when he disappeared from Capitol Hill citing "exhaustion."

Later statements from Jackson's office indicated the condition was more severe, citing "physical and emotional ailments" the lawmaker "has grappled with ... privately for a long period of time."

The episode has sparked some debate between about whether elected officials have an obligation to tell voters about their medical condition and treatment status.

Meanwhile, Jackson's office is busy laying the groundwork for his reelection campaign.

"The congressman also said he expects to be home soon," Jackson's chief of staff, Rick Bryant, told Crain's Chicago Business last week. "He is looking forward to getting back to work; and he fully expects to be running for re-election in the fall."

Rep. Emanuel Cleaver (D-Mo.), chairman of the Congressional Black Caucus, said recently that Jackson is recovering well and is expected back on Capitol Hill.

"He's lost some weight," Cleaver told The Hill, "but he's doing good."

—This story was updated at 3:40 p.m.