By Brooke Katz

FORT WORTH (CBSDFW.COM) – It was last December 15 when Nancy Navarro started feeling sick.

At first she thought it was the flu, but her symptoms got worse.

READ MORE: North Texas Seeing Plenty Of COVID-19 Vaccine Supply With No Wait Lists

” I started feeling like weak,” Navarro said. “I started passing out.”

Navarro was diagnosed with COVID-19 but wasn’t sick enough to be in the hospital. More than two months later, she is still dealing with body aches, occasional fevers, hair loss and loss of smell.

It’s these sorts of cases that are now at the heart of a new study by National Institutes of Health. The goal is to ultimately identify the cause of these long hauler cases, along with treatment and prevention methods.

“We’re not really sure the cause of this,” said Dr. David Winter with Baylor University Medical Center. “We can’t find the virus in the bodies; the immune system seems to be working okay.”

Dr. Winter said while Long Hauler’s syndrome isn’t common, it can affect people of all ages.

READ MORE: 'Nobody Should Get Away With Murder': Family Continues Search For Answers After Father Killed In Suspected Road Rage Shooting In Dallas

Navarro’s only underlying condition is asthma.

“The most prominent symptom typically is fatigue,” Dr. Winter said. “Some folks talk about a brain fog, trouble concentrating, trouble remembering, maybe some confusion.”

According to the NIH, in some of these cases the symptoms persist for months.

They can range from mild to incapacitating.

The prolonged sickness can also take a toll on a patient’s mental health. Nancy has been dealing with depression not knowing if she will ever feel like herself again.

MORE NEWS: Stimulus Check Latest: Is A Fourth Relief Payment Coming?

“I want to take care of my kids,” Navarro said. “I want to be there for my kids, but I can’t. I don’t know what to do.”