U.S. Sen. John Fetterman, D-Penn., remains hospitalized in Washington, D.C. Thursday night after feeling lightheaded while attending a Democratic retreat in the nation’s capital on Wednesday. 

Fetterman, who suffered a stroke during his campaign in May 2022, stayed another night at George Washington University Hospital to undergo testing. His office said Thursday night that an MRI and tests conducted so far have come back negative for another stroke or a seizure.

Though there haven’t been any signs of a seizure thus far, Communications Director Joe Calvello said Fetterman was still being monitored with an electroencephalogram (EEG) – an instrument that measures brainwaves.

Calvello did not share details on when Fetterman might be released, but had said late Wednesday that he was “in good spirits and talking with his staff and family.”

SEN. JOHN FETTERMAN HOSPITALIZED AFTER ‘FEELING LIGHTHEADED’ AT SENATE DEMOCRATIC RETREAT

Pennsylvania Democratic Senate candidate John Fetterman participates in a debate with his GOP challenger Dr. Mehmet Oz on Oct. 25 in Harrisburg, Penn. (NewsNation)

In November, the 53-year-old was elected to replace now-retired Republican Pat Toomey in the U.S. Senate. He defeated celebrity heart surgeon and GOP nominee Dr. Mehmet Oz by five percentage points, flipping a seat that was crucial in the Democrats’ efforts to hold the Senate majority.

The Associated Press reported more than $300 million was spent during the campaign, making it the most expensive Senate race in 2022.

Two days before the state’s Democratic primary on May 15, Fetterman experienced what he later described as a near-fatal stroke. His campaign took a backseat for a few months as he recovered from having a pacemaker with a defibrillator implanted to manage two heart conditions, atrial fibrillation and cardiomyopathy.

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When he fully returned to the campaign trail, Fetterman refused to release his medical records and reportedly wouldn’t allow his doctors to answer questions from reporters, though he insisted his doctors said he could fully recover.

Pennsylvania Democratic Senate candidate John Fetterman particpates in a debate with his GOP challenger Dr. Mehmet Oz on Oct. 25 in Harrisburg, Penn. (NewsNation)

During the months leading up to the November election, Republicans, including Oz, publicly questioned if Fetterman was honest about the effects of his stroke and wondered if he was in a place to serve as senator.

As a result of the stroke, Fetterman has struggled with auditory processing disorder, a common aftereffect that can leave a person unable to speak fluidly. It can also alter a person’s ability to quickly process spoken conversation into meaning.

Those effects were noticeable during the campaign’s only debate in the fall when Fetterman struggled to complete sentences while jumbling words, which raised more concerns about his ability to serve if elected.

During his election night victory speech 15 days later, Fetterman told cheering supporters he ran for “anyone that ever got knocked down that got back up.”

Democratic Senate candidate John Fetterman speaks to supporters during an election night party at StageAE on Nov. 9, 2022 in Pittsburgh, Penn. (Jeff Swensen/Getty Images)

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Before being elected to the U.S. Senate in 2022, Fetterman served as the state’s lieutenant governor from 2019 to 2023 and mayor of Braddock, Penn., from 2006 to 2019.

The Associated Press contributed to this report