As Cassandra Jackson watched her 10-year-old son Johnny splash around in their neighborhood pool last week, she had no reason to believe anything was wrong -- let alone that her son was slowly drowning.
"He seemed to be fine," Jackson, 41, told ABCNEWS.com from her home in Goose Creek, S.C. "I noticed nothing out of the ordinary, other than him taking a little bit of water in and coughing and then calming down."
Jackson estimated that Johnny had been in the pool for 45 minutes and had been wearing floatation devices on each arm, in addition to being monitored by an adult in the pool, as well as herself and a friend watching from pool chairs nearby.
But less than two hours after getting out of the pool, Johnny had defecated in his pants twice and was complaining of being tired.
After being bathed and dressing himself, Johnny walked to his bed unaided, leading his mother to believe that he was simply tired from playing in the water.
But shortly after leaving him to nap, Jackson discovered her son unconscious and his face covered in a foam-like substance.
"My friend went back into the room where Johnny was sleeping and noticed what appeared to be cotton balls stuffed in his nose," Jackson said of what turned out to be the foam from his nose and mouth. "She asked if I put them there and I said no -- I went in and saw him and screamed for help.
"I rolled him over and his body was very limp and I realized he'd soiled himself again and was very purplish-blue looking," said Jackson, who then called 9-1-1. "His tongue was really swollen, too."
Johnny suffered from cardiac arrest on the way to the hospital, his mother said, and was pronounced dead upon arrival.
Berkeley County Coroner Glenn Rhoad examined Johnny's body after the incident and told ABCNEWS.com that the preliminary autopsy showed the cause of death was asphyxiation due to drowning. Rhoad added that the boy had a lot of water in his lungs.
While Johnny had been diagnosed with Attention Deficit Disorder and autism, there is no reason to believe that either condition had anything to do with his death, the coroner said.
How Johnny managed to walk out of the pool and into his bed, communicating with his mother along the way, seems mysterious -- but doctors said Johnny may have suffered from a sort of secondary drowning or near drowning, as some refer to it.
"With primary drowning, you inhale water and you can't breathe and you die right away," said Stephen Epstein, a spokesman for the American College of Emergency Physicians. "But with secondary drowning, you die because of a secondary injury to the lung caused by a small amount of the water getting into the lung."
Johnny would have only had to inhale four ounces of water to drown, and even less to injure his lung enough to become a victim of secondary drowning, Epstein said.
"Depending on what's in the fluid, it can have numerous effects on the lung," said Epstein, who practices at Boston's Beth Israel Deaconess Medical Center. "One of the things that keeps the breathing bubbles in your lungs -- alveoli -- open is a chemical called surfactant, which can get diluted [when fluid enters the lungs]."
What results when the surfactant is diluted and the lung is not working properly, said Epstein, is that the body's natural reactor kicks in and sends other fluids from your body to help -- flooding your lungs with fluids.