Pennsylvania Sen. John Fetterman receiving treatment for clinical depression at Walter Reed National Military Medical Center

BETHESDA, Maryland– Pennsylvania Senator John Fetterman checked into a Washington hospital Wednesday “to receive treatment for clinical depression,” his chief of staff said Thursday.

“While John has suffered from off-and-on depression throughout his life, it has only gotten worse in the last few weeks,” Adam Jentleson said in a statement.

Jentleson said Fetterman was briefed Monday by Congressional Attending Physician Dr. Brian P. Monahan, who recommended “inpatient treatment” at Walter Reed Hospital. “John has consented and is being treated on a voluntary basis.”

“After examining John, Walter Reed’s doctors told us that John is getting the care he needs and will be well soon,” Jentleson said.

Fetterman, a Democrat, won his midterms seat in November. During the campaign, he suffered a stroke, which his doctors said was due to an irregular heart rhythm that led to a clot.

Recovering ahead of the election, he returned to the track, albeit with limited appearances. After the stroke, he worked with a speech therapist and also had problems with auditory processing that required the use of closed-captioned devices.

“He has no work restrictions and can work full-time in public office,” his doctor said of his campaign in October.

Last week, Fetterman was hospitalized for several days of observation after feeling light-headed, although his aides said tests had ruled out seizures or another stroke.

Experts say that clinical depression isn’t necessarily just about feeling down or unhappy, it’s more than that.

“Clinical depression is a brain disorder that affects almost every aspect of a person’s ability to function,” said Mark Friedlander, chief medical officer of Universal Health Services’ Behavior Health Division.

Friedlander says a stressful job can affect any illness, whether it’s medical or mental.

“In the case of Mr. Fetterman, we are talking about clinical depression that may be related to the recent brain injury but is affecting his ability to function,” Friedlander explained.

A source close to Fetterman, who spoke on condition of anonymity, told ABC News that his current hospitalization was not directly linked to the stroke he survived. However, this source said it could be related to the separate incident last week.

He wasn’t eating regularly and “he was doing his job but he just seems absent,” the source said.

“It’s a disease — it’s a different disease,” the source said. After the stroke, Fetterman “was still himself. He wasn’t himself in the last few weeks.”

“It’s not at all uncommon for someone to start recovering from a physical illness, or to make a full recovery from a physical illness and then be hit by the aftermath,” said Janine Mariscotti, assistant professor of social work at La Salle University.

She has worked in adult mental health for the last 30+ years.

She realized how important it was that Fetterman knew something was wrong. Mariscotti says depression is treatable, and if more public figures speak up, we can break down barriers around mental health.

“Most people who are hospitalized for depression come out of the hospital fine and continue to lead their lives very effectively,” Mariscotti said.

Fetterman’s family doesn’t have a schedule for inpatient or outpatient care, but believes it will be “weeks, not months — not days” that he’s likely to be away from the Senate.

“Depression is easily treatable. Many people do not seek treatment because of the stigma. … What John Fetterman is doing right now is exactly what people should be doing when they have mental health issues,” the source said.

Senate Majority Leader Chuck Schumer tweeted in support of Fetterman, writing, “Glad to hear it [he] gets the help he needs and deserves. Like John, millions of Americans battle depression every day. I look forward to seeing him return to the Senate soon. Sending love and support to John, Gisele and their family.”

Some Republicans echoed that. Texas Senator Ted Cruz tweeted that he and his wife “lifted John up in prayer. Insanity is real & serious and I hope he gets the care he needs. Regardless of which side of the political aisle you are on, please respect his family’s request for privacy.”

Fetterman’s wife, Gisele Barreto Fetterman, wrote on Twitter: “This is a difficult time for our family so please respect our privacy. For us, the children come first.” She and the senator share three children.

“Take care of yourself. Hold on to your loved ones, you are not alone,” she wrote, while praising her husband for “asking for help and getting the care he needs.”

“After what he’s been through over the past year, there’s probably no one less eager to talk about their own health than John,” she wrote. “I’m so proud of him.”