A woman traveling from Tampa, Florida, to Chicago on Tuesday died mid-flight en route to O'Hare International Airport, leading at least one passenger to question whether the airline properly handled the emergency.

The 59-year-old Chicago woman, who reportedly had high blood pressure and diabetes, became unresponsive during the Spirit Airlines flight. A concerned passenger said she appeared uncomfortable and was drifting in and out of sleep.

"It was just horrible," Katharine Katzenberger, the passenger, said. "There was a tiny bit of moaning, but not anything that anyone else would hear. I looked over and asked if she was ok. It looked as if she was talking in her sleep, her eyes remained closed. She didn't respond to me when I asked her that."

Katzenberger said that other passengers expressed concern and alerted flight attendants to the woman's condition, but the doctor on board was not allowed to help because the plane had just begun its descent, which took about 20 to 30 minutes.

"The captain is always allowed to do whatever they think they need to do in an emergency to keep everyone safe," aviation specialist Rob Mark said.

A Spirit Airlines spokesperson told NBC 5 that the doctor said the defibrillator was operational, but he wasn't able to use it on the passenger. He instead performed CPR for several minutes while the crew provided oxygen, but the woman remained unresponsive.

The plane was met with medical personnel immediately when it landed, and the woman was taken to the hospital where she was pronounced dead due to natural causes.

The medical examiner's office confirmed that the woman had high blood pressure and diabetes.