Mother of 2 dies mysteriously while on flight back from Dominican Republic

Family and friends of an Indiana mother said they were shocked and stunned by her sudden death as she was aboard a flight returning from a vacation in the Dominican Republic last week.

Investigators in Turks and Caicos said they are investigating the Feb. 28 death of Stefanie Smith, who was onboard the American Airlines flight from the Dominican Republic to North Carolina. Smith, 41, fell ill mid-flight which prompted an emergency landing in Turks and Caicos, where she was transported to a hospital and later died, the Turks and Caicos police said in a statement.

A cause of death was not immediately determined and medical examiners are conducting an autopsy, the police said.

Smith was vacationing with her boyfriend for five days and seemed healthy right before the flight, according to her friend, Maria Yannotti, who was also on the trip.

"She loves going to the gym every day, even while we were in the Dominican. She made it a point to get up every morning to go to the gym and run on the beach," Yannotti, who traveled to the Dominican Republic separately, told ABC News.

Smith's boyfriend was sitting next to her on the flight and said her eyes rolled back and she started convulsing, according to Yannotti.

A doctor and nurses on board the plane helped to administer CPR to Smith before the plane made an emergency landing, according to a source with knowledge of the investigation.

Smith was the mother of two children, an 18-year-old son and a 16-year-old daughter, according to her brother, Chris Volz. Volz told ABC News that he was not aware of his sister having any preexisting health conditions.

"She was a special person. ... Her kids really ... love her a lot, and I know she loved them," he said. "And so it's tough."

ABC News' Anselm Gibbs contributed to this report.