Clayton Osbon, the pilot who was subdued aboard JetBlue flight 191 after going into a rage, may have had a toxic reaction to infection, drugs or even an encephalitic event caused by a brain tumor.
On a routine flight from JFK Airport in New York to Las Vegas, Osbon "began acting erratically, flipping switches in the cockpit and appearing confused," according to sources.
"The captain of the plane just went berserk," passenger Wayne Holmes told ABC. "He came out of the other end of the plane -- came running back to the cockpit and he was shouting out these numbers -- 500 something. He started banging on the cockpit door."
A passenger subdued Osbon, a veteran captain, and the flight was diverted safely to Amarillo, Texas. There were 131 passengers and six crew members aboard.
Osbon has been "suspended" until questions about his medical condition have been cleared up, ABC has learned.
For now, authorities are saying Osbon, 49, suffered a panic attack. Yet there are still many unanswered questions.
"The JetBlue pilot's behavior is much more than a simple panic attack, which might occur as a result of a phobia or panic disorder," said Una McCann, director of the Anxiety Disorders Clinic at Johns Hopkins Medical Institution.
At one point, when a flight attendant asked Osbon what was wrong, he frantically replied, "You'd better start praying right now," and he then began shouting about Al Qaeda, a bomb, and warning that the plane would crash, according to passengers on the flight.
"Rage is not a typical feature of uncomplicated panic, so there is clearly something additional that took place here," said McCann. "While JetBlue may not be misinforming the public when they say their pilot had a panic attack, they are not telling the full story."
Panic attacks can also occur in conjunction with paranoid psychosis and post-traumatic stress disorder flashbacks, but McCann said that Osbon's behavior looked more like a drug-induced toxic reaction.
Even a simple fever from an infection can cause hallucinations and confusion, she said. Also, psychotic disorders like schizophrenia are more apt to surface in the teens and 20s. Osbon was 49.
The pilot remains in custody of authorities while under the care of medical professionals in Amarillo. He is expected be released from the medical facility later this week after a 72-hour hold, according to airline sources.
The rest of the flight crew has been taken off duty to help with the investigation and to decompress after the incident, sources said.
More than 40 million Americans suffer from panic attacks, which are characterized by a sudden and repeated fear of disaster or losing control, even when there is no real danger, according to the National Institute of Mental Health. Anxiety disorder sufferers are mostly women.
Unlike the relatively mild, brief anxiety caused by a stressful event, anxiety disorders last at least six months and can get worse if they are not treated.
They can also occur along with other mental and physical illnesses, including substance abuse.
McCann said that doctors should be able to determine the cause of the pilot's erratic behavior during the next few days.
While hospitalized Osbon is expected to undergo toxic screening, including blood counts to make sure he has no infection, vital signs to see if his temperature is within normal ranges and a neurological exam that might include a scan of the brain, according to McCann.
"A brain tumor could do this," she said of his erratic behavior.
"They will also investigate things that can impact the central nervous system, like drugs," said McCann. "Drugs prescribed over the counter, and, in particular sleep deprivation, can turn someone over the edge."
Doctors will also look for use of stimulants for a potential toxic reaction. "Pilots often have weird shift work," according to McCann, and stimulant abuse is said to be prevalent.
A "horrible trauma" might have triggered such an outburst, according to McCann. But typically flashbacks only last 10 to 15 minutes, she said, not the extended length of time Osbon was reported to have been forcibly subdued.
"If you had just the right circumstances -- no sleep, taking stimulants and a history with a PTSD trigger, he could have had weird flashbacks."
Another suspicious element is that Osbon was reported to have had visual hallucinations during the incident, which are not typical in psychotic breakdowns. Those with schizophrenia more typically have auditory flashbacks and "mental thoughts," according to McCann.
"It sounded like he was seeing things, and that is highly suggestive of an encephalitic event or a brain tumor," she said.
McCann applauded how passengers and crew handled Osbon's outburst. "Those were not ideal circumstances and they were brilliant," she said.
The "hero" passenger -- David Gonzalez -- said he was sitting in the second row of the plane when Osbon stormed out of the cockpit and rushed toward an occupied bathroom.
Flight attendants struggled to control him and Gonzalez, a 50-year-old from Pennsylvania on his way to a security convention, stopped the pilot as he moved in the direction of the plane's emergency exit.
Gonzalez put pressure on Osbon's windpipe and threw him to the floor where he sat on the pilot until the plane safely landed.
Anxiety psychologist Dr. Gregory Jantz, author of the 2012 book, "Overcoming Anxiety, Worry and Fear," said panic is a perfectly plausible in this scenario, especially in this age of terrorism.
Fear of flying is now number three among the top 10 phobias, according to Jantz.
"It has all the characteristics of a common panic attack and we are seeing more and more in our work with celebrities and sports figures and high-profile individuals," said Jantz.
"Professionals are more prone to panic attacks," he said. "One, they are high-performers. If you are a pilot or an athlete, you may be dealing with an underlying anxiety. Eventually, the body says, 'I can't carry this any longer.'"
Two to 5 percent of those who have panic attacks "do step over and lose touch with reality," according to Jantz.
He said the pilot may have had an anxiety disorder for some time.
"And usually, they find ways to self-medicate," said Jantz. "They look for ways to calm themselves and unfortunately, it can be self-destructive."
Fatigue can also trigger a panic attack, he said. "That is very common. People with anxiety disorder tend not to get enough REM sleep and they are in constant fatigue. That adds to the anxiety and can be a ticking time bomb."
Without treatment, panic disorder can get worse and sufferers can be "paralyzed by fear," he said.
But McCann said she believes that an underlying medical condition may explain Osbon's out-of-control behavior.
"If it's one of those toxic-induced things, we will know soon," she said. "I am hopeful for the pilot that it's the cause, because of his lack of prior history and there were no red flags in his exams."
"But if everything is negative and he continues this behavior in a very psychotic way," she said. "That will be a problem."
ABC's Matt Hosford and Christina Ng contributed to this report.