Is Hillary Clinton's blood clot serious? That's the question on everyone's mind tonight after the secretary of state was hospitalized Sunday for clotting that stemmed from a concussion earlier this month. In mid-December, Clinton became dehydrated and fainted. But at the time doctors said the secretary of state's condition was not serious.

Now Clinton spokesman Philippe Reines says Clinton's doctors discovered a clot during a follow-up examination on Sunday. Clinton was admitted to New York-Presbyterian Hospital and will be treated with anti-coagulants. She will be monitored at the hospital for at least 48 hours, Reines said, so doctors can stay informed on a regular basis about the clot and "other issues associated with her concussion."

When the concussion occurred two weeks ago, a senior State Department official said the concussion was "not severe." Clinton, 65, was not hospitalized at the time, but she was asked to work from home. She was also suffering from a stomach virus at the time.

"At the [doctors'] recommendation, [Hillary Clinton] will continue to work from home next week, staying in regular contact with Department and other officials. She is looking forward to being back in the office soon," Reines said two weeks ago.

The secretary of state had been slated to testify in Washington, D.C. about the fatal attack in Benghazi, Libya, in September that killed four Americans. But doctors said she would be unable to go to the Bengazi hearings.

"Secretary Clinton's team contacted Senator Kerry this morning to inform them of the Secretary's concussion," Jodi Seth, spokeswoman for Democratic Sen. John Kerry, Senate Foreign Relations Committee chairman, said at the time. "Senator Kerry was relieved to hear that the Secretary is on the mend, but he insisted that given her condition, she could not and should not appear on Thursday as previously planned, and that the nation's best interests are served by the report and hearings proceeding as scheduled with senior officials appearing in her place."

Rep. Ileana Ros-Lehtinen, R-Florida, who chairs the House Foreign Affairs Committee, didn't hesitate to voice her displeasure about the fact that Clinton didn't testify. "Although I respect Bill and Tom, we still don't have information from the Obama administration on what went so tragically wrong in Benghazi," Ros-Lehtinen said in a statement. "We have been combing classified and unclassified documents and have tough questions about State Department threat assessments and decision-making on Benghazi. This requires a public appearance by the Secretary of State herself."

In the last 12 months, there's been increased talk about Clinton's age because she is widely viewed as a frontrunner for the 2016 election. Yet the secretary of state insists she doesn't plan to run.

"Look, I'm flattered. I am honored. That is not in the future for me, but obviously I'm hoping that I'll get to cast my vote for a woman running for president of our country," Clinton said.

In a CNN/ORC International poll released today 85 percent of Democrats and independents said they would back Clinton if she ran for president. Ninety-three percent of Democratic women said they would support Clinton, while 79 percent of Democratic men said they would cast a vote for her.

"I really don't believe that that's something I will do again," Clinton said about a potential run in 2016. "I am so grateful I had the experience of doing it before. I think there are lots of ways to serve, so I'll continue to serve."

Though Clinton has made a huge impact as first lady, senator from New York and now secretary of state, many pundits believe she would still like to reach higher. Nate Silver believes Clinton would be the Democrats' best shot of extending "their winning streak to three or more terms in the White House."

Some detractors have claimed that Clinton would be too old for a run in 2016. But Clinton told Barbara Walters recently: "I am, thankfully, knock on wood, not only healthy, but have incredible stamina and energy."

Clinton has not been seen in public since she was diagnosed with the concussion on Dec. 13.