How can a person be fine one minute and dead the next?

It happened to Natasha Richardson in March. After hitting her head on a ski slope in Canada, the Tony Award-winning actress was seemingly fine, laughing about being clumsy before heading back to her hotel room.

But a short-time later, Richardson complained of severe head pain and from there her condition deteriorated, she went into a coma shortly after arriving at a Canadian hospital and was taken off life support two days later.

Now, some are wondering if that same fate befell TV pitchman Billy Mays, who died Sunday after suffering a head injury Saturday after the airplane he was on had a rough landing at Tampa Bay's airport.

It's "something we call the ‘talk and die’ syndrome,” Dr. Steven Flanagan, director of Rusk Institute of Rehabilitation Medicine at New York University’s Langone Medical Center, told FOXNews.com at the time of Richardson's death.

“What this implies is that someone hits their head and they are seemingly OK initially," he said. "But then they get a rapid collection of blood — usually called epidural hemorrhage — and that means bleeding between the skull and the brain.”

Fifty-year-old Mays, who joked with a reporter about his head injury after the plane's landing Saturday, apparently told his wife later that night he was not feeling well when he went to bed. He was found dead the next morning.

Related: Did Rough Plane Landing Cause Mays' Death?

Flanagan said a person doesn't always show outward signs of trauma when suffering a head injury.

“When someone has bleeding between the skull and the brain, it basically presses on the brain, and if it presses enough… it can cause substantial damage and even death,” Flanagan said. “And presumably that’s what probably happened to her — but again, we’re speculating.”

Symptoms of an epidural hemorrhage include:

— Headache;

— Loss of consciousness;

— Weakness on one side of the body;

— A change in mental status

If the condition is not treated immediately, the person will fall into a coma and “it’s downhill from there,” Flanagan said.

“So you need to get the injury treated immediately,” he said. “First we would do an emergency CAT scan to find out exactly where the hemorrhage is, and then the patient would need immediate surgery.”

While this demonstrates to use caution when suffering a painful head injury, Flanagan said people should not panic over every little bump and bruise.

“If you bumped your head getting out of the car, this wouldn’t happen to you,” he said. “It would have to be a significant injury.”