(CNN) President Donald Trump has suffered high fever and his oxygen levels have fallen at least twice as he has battled Covid-19, his doctors said Sunday.
Following two briefings from Trump's doctors over the weekend, more details about the course of his Covid-19 illness are emerging -- but some questions still remain.
Since Trump announced his Covid-19 diagnosis on Twitter early Friday morning, his illness has had frequent "ups and downs," White House physician Dr. Sean Conley said during a briefing at Walter Reed National Military Medical Center on Sunday.
On Thursday night and into early Friday morning, Conley said, the President "was doing well with only mild symptoms" and his oxygen level was in the high 90s -- but then late Friday morning, "the President had a high fever and his oxygen saturation was transiently dipping below 94%," Conley said. A normal blood oxygen saturation level is 95% or higher.
The President initially was "fairly adamant that he didn't need" oxygen. "He was not short of breath. He was tired, had the fever, and that was about it," Conley said.
However, the President was given oxygen.
"And after about a minute on only two liters, his saturation levels were back over 95%. He stayed on that for about an hour maybe, and was off and gone," Conley said.
Later that Friday, Conley added, the President was out of bed, moving around the White House residence and had only mild symptoms.
On Friday afternoon, Conley said in a White House letter that Trump received a monoclonal antibody cocktail -- an investigational immune system treatment from the biotechnology company Regeneron -- and had taken zinc, vitamin D, the heartburn drug famotidine, melatonin and a daily aspirin.
Some small studies have indicated famotidine, the active ingredient in Pepcid AC, might help improve recovery from Covid-19 but it wasn't clear if that's why Trump took it.
On Friday evening, the President was transported to Walter Reed National Military Medical Center for evaluation and monitoring. Before leaving for the hospital, Trump recorded a video message announcing that he was being transported.
The President has remained without fever since Friday morning, Dr. Sean Dooley, one of Trump's physicians, said during Sunday's briefing. Doctors have not said whether they have given him fever-reducing medication such as ibuprofen or acetaminophen.
Trump's oxygen level transiently dipped again on Saturday.
"Yesterday there was another episode where it dropped down to about 93%," Conley said on Sunday. "We watched it and it returned back up."
Trump's physicians decided to give him the corticosteroid drug dexamethasone, which has been shown to help patients with Covid-19 and is typically given to patients on supplemental oxygen or ventilation.
In the United States, dexamethasone has been used to treat some Covid-19 patients since early on in the pandemic -- but some doctors previously have warned "it is not a treatment for mild disease."
Dexamethasone is usually used to treat certain forms of arthritis, severe allergies and asthma, among other conditions, including certain types of cancer. Side effects can include upset stomach, headache, dizziness, insomnia and depression. GoodRx estimates the most common version of the drug can cost as little as about $6.
"In response to transient low oxygen levels, as Dr. Conley has discussed, we did initiate dexamethasone therapy, and he received his first dose of that yesterday," Dr. Brian Garibaldi, one of Trump's doctors, said during Sunday's briefing.
"Our plan is to continue that for the time being," Garibaldi said. The President also continued his course of remdesivir -- completing his second dose on Saturday evening.
"He's tolerated that infusion well -- we've been monitoring for any potential side effects, and he has had none that we can tell," Garibaldi said.
That same evening, Trump tweeted a video message from Walter Reed, saying that he is "starting to feel good."
As of Sunday around noon, Trump feels well, Garibaldi said.
Garibaldi added that the President could be discharged as early as Monday.
"He's been up and around. Our plan for today is to have him to eat and drink, be up out of bed as much as possible to be mobile," Garibaldi said on Sunday. "And if he continues to look and feel as well as he does today our hope is that we can plan for discharge as early as tomorrow to the White House where he can continue his treatment course."
As Trump's course of illness continues, there are questions that still remain around his condition.
During Sunday's briefing, Conley offered no detail about what X-rays or CT scans have shown about whether there has been any damage to the President's lungs.
"We're tracking all of that. There's some expected findings, but nothing of any major clinical concern," Conley said, not explaining whether they were expected findings in a normal patient or a Covid-19 patient.
And while Conley said Trump experienced a "high" fever, he has not given details of how high Trump's fever went, or what his current temperature is.