Fetterman, who has struggled with the aftereffects of a stroke he suffered in May, checked himself in Wednesday night, it said.

“While John has experienced depression off and on throughout his life, it only became severe in recent weeks,” his chief of staff, Adam Jentleson, said in a statement.

Fetterman was evaluated Monday by the attending physician of Congress, Dr. Brian P. Monahan, who recommended inpatient care at Walter Reed, Jentleson said.

“John agreed, and he is receiving treatment on a voluntary basis,” Jentleson said. “After examining John, the doctors at Walter Reed told us that John is getting the care he needs, and will soon be back to himself.”

Fetterman, 53, is in his first weeks as a U.S. senator after winning the seat held by now-retired Republican Pat Toomey in a hard-fought contest against GOP nominee Dr. Mehmet Oz.

Fetterman overcame a stroke days before last May’s primary election and spent the last five months on the campaign trail recovering from the stroke.

Last week, Fetterman stayed two days in George Washington University, checking himself in after becoming lightheaded. Fetterman’s office has said tests found no evidence of a new stroke or a seizure.

He continues to suffer the aftereffects of the stroke, in particular auditory processing disorder, which can render someone unable to speak fluidly and quickly process spoken conversation into meaning.

The stroke nearly killed him, he has said.

Fetterman underwent surgery to implant a pacemaker with a defibrillator to manage two heart conditions, atrial fibrillation and cardiomyopathy, and spent much of the summer recovering and off the campaign trail.