Littrell explained on his Web site how Baylee was tested for various infections, including strep throat and hand, foot and mouth disease, before he was diagnosed with atypical Kawasaki syndrome.
The ailment causes inflammation in blood vessels throughout the body and the most serious cases are when blood vessels surrounding the heart become inflamed. Kawasaki syndrome is a leading cause of acquired heart disease in the United States, ABC News said.
"He's never been sick," said Baylee's mother, Leighanne Littrell. "(When he started exhibiting symptoms) it kind of blew us away and from then on things escalated."
ABC News said doctors weren't sure what the boy had until his mother requested an echocardiogram, which revealed the arteries around Baylee's heart were inflamed. The child was then diagnosed with Kawasaki syndrome and treated at the Scottish Rite Children's Hospital in Atlanta from which he has since been released.
Leighanne Littrell said her son was so good in the hospital he was given Batman and Superman outfits as a reward.
"He walked out (of the hospital) as Batman," ABC News quoted her as saying. "He's our hero."