President Trump was discharged from Walter Reed National Military Medical Center and returned to the White House Monday evening. He gave reporters a double thumbs up on his way in the doors and his doctors earlier today said "he's up and back to his old self."

But he's a few days into his diagnosis with COVID-19, a novel disease that doctors are still learning how best to treat. And medical experts say, he may still be in a danger zone.

At today's press briefing, though largely optimistic about the President's condition, his physician Dr. Sean Conley said he "may not be out of the woods yet."

"I would also agree with the medical team that just because he's going home, he's not completely out of the woods," says Dr. Faisal Masud, medical director of critical care at Houston Methodist Hospital. "He has to demonstrate continuous success and no lung issue because, you know, some of these patients have long-term lung impact."

At Monday's press briefing, Conley said Trump's oxygen levels were healthy and he was breathing well, but he declined to answer a reporter question about whether there is evidence of pneumonia on the President's lung scans.

The President did have a fever, fatigue and a mild cough late last week, but hasn't had fever in 72 hours, his doctors said.

It's a good sign that he was well enough to be discharged, says Colleen Kraft, an infectious disease physician and associate chief medical officer at Emory University Hospital in Atlanta. But even patients with COVID-19 that have mild symptoms at first can suddenly worsen, she says.

"Individuals that have mild disease to start out with, just mild symptoms, they can in a week or so feel worse, worse enough to be in an ICU," she says.

However, she notes, most people with mild symptoms don't get the kind of aggressive treatment that Trump received. He's received an experimental antibody treatment, a course of remdesivir and the steroid dexamethasone, all treatments generally reserved for patients hospitalized with severe symptoms. So, she says, it's hard to know what to expect in the coming days.

"It's possible that [the interventions] could make him better sooner," she says. "[But] we don't know really what happens to people that have mild disease and then get treatment with antibody medications, antivirals or steroids. I think we're sort of a little bit in a data-free zone, where we're not sure."

And, Kraft adds,the President's medical team "is going to be very vigilant about his symptoms" in the coming days. "So he'll be getting his vitals checked at least every day or every couple times a day in order to make sure nothing is happening." He will also need to complete his course of medications — the Remdesivir and dexamethasone, she adds.

Masud notes that recovering COVID-19 patients who were hospitalized need to be closely monitored in case they get worse, especially older adults.

Some of the common symptoms among people who take a turn for the worse are: confusion, issues with memory, fatigue and not being able to catch their breath, he says.

The above symptoms, if they presented themselves could also indicate a secondary infection, he adds, because a small percentage of COVID-19 patients go on to develop secondary bacterial infection.

Though Trump is not on oxygen now, his physicians did disclose he had "several little temporary drops in his oxygen" and took supplemental oxygen twice.

Masud says if he had a patient with Trump's profile — male, over 70 years and overweight — who was hospitalized for a few days and received aggressive treatments, he would want to monitor the patient's oxygen levels closely even after they went home.

"We like to watch them for a day or two to make sure there's no relapse because we've had patients who relapsed also and required oxygen, especially when they become active ... they get tired and they can't catch their breath."

Masud says he would also monitor markers of inflammation, "to see if they're trending downwards nicely or not." That would suggest the infection is going away.

When speaking with reporters, Conley said the President would be closely monitored by the medical team at the White House at least through the weekend. "If we can get through Monday with him remaining the same or improving, better yet, then we will all take that final, big sigh of relief," he said.

Masud says it's important for patients recovering from COVID-19 to get plenty of rest and adequate sleep, as "one of the key things which has been shown to help patients recover is having good sleep, long duration of sleep," he says.

With a grueling election season ahead of him, lack of sleep and adequate breaks could hurt Trump's recovery, he adds. "And I would not wish for the President to have any of those setbacks."

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