Pope John Paul II is clearly a survivor. The 84-year-old pontiff has survived a gunshot wound from an assassination attempt, a bowel tumor, an appendectomy and a fractured thigh. He also has Parkinson's disease, and his stooped posture may be a sign of osteoporosis.

But it is this latest malady -- reportedly a bout of influenza coupled with breathing difficulties -- that has medical experts outside the Vatican most concerned, reported WNBC-TV in New York.

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"It's potentially a disaster," said Dr. Murray Rogers, of Lenox Hill Hospital in New York. "An older individual or older patient, even if they enjoyed good health, becomes more and more serious the older the patient gets."

The pope was hospitalized Tuesday night after he suffered a spasm of his larynx, or voice box. That's potentially serious, because the larynx controls the passage of air into the trachea and lungs.

When viewed from the mouth, you see a small opening between the vocal cords. If they spasm and close, it's a feeling of choking or suffocation -- much like when something goes down the wrong pipe.

Again, this is more serious in the elderly.

"If a laryngospasm keeps up and your oxygen saturations are low, for an elderly person, it could end up in a heart attack," said Dr. Jordan Jopsephson, of Lenox Hill Hospital. "There are some grave consequences of having repeated laryngospasm and the flu in an elderly patient. You really need to be seen by your physician immediately, and then, if you need to be admitted to the hospital for observation, for admission for oxygen and intubation."

There's no indication that the pope has been on a ventilator, and official Vatican statements said he is recovering well.

But experts warn that the pontiff's generally weakened state makes it harder to fight off infections. Plus, his Parkinson's disease makes muscle control and breathing difficult, and his stooped posture makes it harder for him to cough, which keeps him from clearing his lungs of pneumonia-causing bacteria.

"He's a critically ill man," Rogers said. "It's a very serious situation, but he has a good chance of full recovery -- and if he does recover, it will be a full recovery."