A child who’s coughing and having trouble breathing hours after nearly drowning should be taken to the emergency room, doctors say. A rare but sometimes deadly aftershock of near-drownings are so-called secondary drownings as the body tries to expel water from the lungs. Most episodes of secondary drownings occur seven or so hours after mishaps in the water but may happen as soon as two hours afterward — with the danger passing in 24 to 48 hours.

“They may be completely fine,” Louis Profeta, an emergency room physician at St. Vincent Health in Indianapolis told Fox 5. “The lungs start to fill up with water. It’s not necessarily the water they’ve inhaled, but it’s a biological, physiological response to near-drowning.” That response occurs as the larynx in the throat relaxes to allow water into the lungs, with sudden mood swings also a symptom of trouble.

“If you’ve had a child that’s had a near-drowning episode, I would certainly hope that you’d bring them into the emergency department,” Profeta said. “But if they look fine and you’re at home and all of a sudden the child takes a turn for the worse, starts coughing a lot, complaining of having trouble breathing, you need to bring them immediately to the emergency department.”

Having seen many such cases for years, Profeta says children may appear listless and sick, as if suffering from an asthma attack or other respiratory illness — and suggested that parents “trust their gut.” Symptoms progressed quickly for 10-year-old Johnny Jackson of Goose Creek, S.C., six years ago when his mother Cassandra sent him to bed, fatigued from a day of swimming.

“My friend went back into the room where Johnny was sleeping and noticed what appeared to be cotton balls stuffed in his nose,” Jackson told ABC News, referring to her son’s foaming of the 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,”

Johnny’s tongue had been swollen too, she added. While no government keeps statistics on such secondary drownings, experts generally recognize that small amounts of water inhaled into the lungs may pose a later threat as fluid accumulates hours after the exposure, with death a possibility.

Among all drownings in the United States, the Centers for Disease Control and Prevention says children between the ages of 1 and 14 account for some 20 percent of victims. More than half of drowning victims who received emergency room care required further hospitalization, with some experiencing brain injuries debilitating to varying degrees. According to the data, 80 percent of drowning victims are men and boys, with African-American boys three times as likely to drown as their white counterparts.

More than 3,500 Americans drown every year, or about 10 per day.