JACKSONVILLE, Fla. -- A 10-year-old boy drowns while lying down in his own bed, bringing attention to what doctors call dry drowning.

Cassandra Jackson's son Johnny died hours after going for a swim in his neighborhood pool.

"I feel like someone reached in and grabbed my heart and just yanked it out," Jackson said.

Johnny's death was caused by asphyxiation. The 10-year-old had too much water in his lungs. It may sound strange, but it's called dry drowning.

"The term sounds so contradictory -- drown and dry," said Dr. Harold Laski.

Laski said dry drowning is not as uncommon as people might think. He said 15 percent of all drownings happen when the victim is not in the water.

"You don't even need much water -- just a little bit of water that hits the flap that opens and closes to allow you to either breathe or eat," Laski said.

In Johnny's case, the boy went swimming and it wasn't until hours later when he started showing signs that something was wrong.

His mom said the 10-year-old soiled himself, started talking slowly and was drowsy. Johnny laid down to take a nap, and an hour later he died.

"He was talking, walking -- it was an hour later that he passed away," said Jackson.

Three important signs of dry drowning for which parents should watch include difficulty breathing, extreme tiredness and behavioral changes.

All of the symptoms are a result of reduced oxygen flow to the brain. Victims can be treated but need to get to an emergency room as quickly as possible.