During Senator Feinstein’s bout with shingles, which kept her away from the Senate for 10 weeks, the senator also battled encephalitis, a rare complication that can affect memory and language capabilities, according to new reporting.

Ms. Feinstein suffered from encephalitis as well as a sort of facial paralysis known as Ramsay Hunt Syndrome during absence earlier this year, the New York Times reported. Encephalitis is a swelling of the brain that can cause headache, sensitivity to light, and mental confusion, among other issues, according to Johns Hopkins University’s School of Medicine.

These previously unknown details have once again raised serious concerns over the senator’s health, particularly after an incident reported earlier this week when she appeared to not recall her absence from the Senate.

“No, I haven’t been gone,” Ms. Feinstein responded when asked about her absence, according to reporting by Slate. “No, I’ve been here. I’ve been voting,” she said, adding, “Please. You either know or don’t know.”

Since then, Ms. Feinstein has faced another call for her resignation from a fellow California Democrat, Representative Ro Khanna, who was the first member of Congress to do so during her absence.

“I have a lot of respect for Senator Feinstein and I am wishing her the best in her return and recovery,” Mr. Khanna wrote in an email to SFGATE. “That being said, I stand by my call for her to resign.”

According to reporting from Politico, the eldest daughter of Speaker Pelosi, Nancy Corinne Prowda, has taken a role in helping the senator since her return to work last week.

While Ms. Pelosi and Ms. Feinstein are longtime friends, some have speculated that Ms. Pelosi is also angling to help Ms. Feinstein remain in office through the rest of her term.

In a statement to the San Francisco Chronicle, Ms. Pelosi’s office said the lawmakers “have been friends since long before their service in Congress — and their friendship is personal, not political.”

Still, some have speculated that Ms. Feinstein’s ability to remain in her seat through the end of her term could be instrumental in giving Representative Adam Schiff, an ally of Ms. Pelosi’s, an upper hand in the coming California Democratic Senate primary.

Ms. Pelosi has already endorsed Mr. Schiff to be Ms. Feinstein’s successor, though he’s not the only Democrat with a shot at winning the seat.

A liberal firebrand, Representative Katy Porter, has also announced that she will be running for the seat. More relevant to the situation with Ms. Feinstein, though, is Governor Newsom’s promise to appoint a Black woman to the seat.

That’s because Representative Barbara Lee would probably be the best fit for the job. If Ms. Lee was appointed, though, she would enjoy a substantial advantage heading into the primary, throwing a wrench in Mr. Schiff’s plans to succeed Ms. Feinstein.

Ms. Feinstein’s office has declined to publicly comment on the situation, but did release a statement to the Times on her return to the Senate and her ability to perform her duties.

“I’m back in Washington, voting and attending committee meetings while I recover from complications related to a shingles diagnosis,” Ms. Feinstein said in a statement. “I continue to work and get results for California.”