Studies into Excited Delirium include a 1998 report in the Canadian Medical Association Journal, a recent book and a 1993 report in a U.S. forensics periodical.

When police arrived at the Right Spot bar in downtown Moncton on May 5, 2005, Kevin Geldart was acting strangely. The 34-year-old had a history of bipolar disorder and had somehow walked away from the psychiatric unit of a nearby hospital earlier that night.

Police said Geldart was acting combative and violent, and seemed to possess superhuman strength. However, witnesses testified Geldart was talking to himself in a corner but wasn't aggressive to those around him, according to his sister, Karen.

Officers used pepper spray and a Taser, as many as four times, to try and subdue the six-foot-six, 300-pound man. Then four officers pinned Geldart down, tied his feet and cuffed his hands. It was then that the police noticed Geldart had stopped breathing. He was later pronounced dead at a Moncton Hospital.

Fast forward to Oct. 14, 2007.

A similar scene, except this time the setting is at the other side of the country — Vancouver International Airport.

Robert Dziekanski had just flown in from Poland and couldn’t speak a word of English. The 40-year-old came to start a new life in Canada with his mother and was waiting in the customs area for her to pick him up.

By 1:00 a.m., he had been waiting more than eight hours. For reasons that are still unclear, he never saw her.

It was at that point that Dziekanski started acting confused and agitated and began throwing around computer equipment. RCMP were called to the scene.

Maureen Taylor reports on the medical discussion over excited delirium (Runs 2:36)

According to an eyewitness video, four officers approached Dziekanski, who stood calmly while talking to them. Dziekanski then walked away and stood by a wall.

Seconds later, a loud crack is heard. Dziekanski is shocked by a Taser, wails and collapses to the ground. The officers kneel on top of him, pinning him down as he struggles. He died minutes later.

In both of these sudden deaths, what's the culprit?

A rare condition

Some psychologists say the cause is a rare condition called "excited delirium" and not the obvious common element — the use of a Taser.

According to some psychologists, a person with excited delirium acts agitated, violent, sweats profusely and is unusually strong and insensitive to pain. Then, the victim's heart races and eventually stops beating.

A coroner’s inquest into Geldart’s death concluded he was suffering from excited delirium on the night he died.

And while the B.C. coroner’s service has not yet determined what killed Dziekanski — an autopsy failed to reveal a clear cause — RCMP have speculated the 40-year-old was also suffering from excited delirium.

"This is not due to a Taser," says Deborah Mash, a neurology professor at the University of Miami who has been studying excited delirium for 20 years. "This is in the brain and they die because the mechanisms that control the heart and the lungs fail."

In recent years, the condition has been showing up in coroner’s reports around the world as a cause of death.

Yet, this condition is the subject of fierce debate in psychiatric circles.

Dr. Ian Dawe, the director of psychiatric emergency services at St. Michael’s Hospital in Toronto, says excited delirium is not a recognized mental disorder.

In fact, the term is not listed in the Diagnostic and Statistical Manual of Mental Disorders of the American Psychiatric Association, a handbook for professional psychologists and psychiatrists.

"The term 'excited delirium' has been co-opted over the course of popular culture, perhaps over the past 15 to 20 years, to refer to this group of people who experience agitation and violence," Dawe told CBC News.

Delirium on its own, however, is a well known disorder, which is marked by confusion and agitation and can be associated with violence. It's usually triggered by another factor such as drugs or a predisposed medical illness, says Dawe.

He's not sure where the prefix "excited" comes from. And in his experience, he says it is uncommon to see patients with delirium suddenly die.

"It is rare. Certainly we don’t see it happen in hospitals per se because of the way that we are approaching things."

First reported in the 1800s

According to Dr. Mash, however, individuals with excited delirium symptoms were first reported in the 1800s by Dr. Luther Bell.

Bell and his team described it as "exhaustive mania" or "agitated delirium," Mash says. "People would present with this bizarre behaviour — extremely agitated, incoherent speech — really like a manic phase. Then, all of a sudden they become hot and they would have an autonomic system failure. Their cardio-respiratory system would fail and they would collapse."

But the key study that described the phenomenon was released in 1985 by Dr. Charles Wetli, Mash said. It looked into excited delirium and cocaine abuse in Miami, which was experiencing the first wave of the crack-cocaine epidemic that swept through North America.

Mash said Wetli outlined the same set of behaviours — agitation, superhuman strength, high pain tolerance — and determined that the condition could be triggered by drugs, alcohol or other stimulants.

"These can sort of trip the switch in vulnerable individuals," she said. "You can also see this with alcohol withdrawal, you can see it in psychiatric patients. It's always the same pattern."

However, these substances don't need to be present to trigger the condition. Excited delirium can also manifest itself in vulnerable patients who are under unusual stress or are sleep-deprived, she says.

Sudden death

While the underlying mechanism of this disease is still unclear, this brain-based illness can lead to sudden death, Mash notes.

"The reason people question it is because law enforcement is involved," she argues. "When Dr. Bell described these conditions in the mid-1800s, law enforcement was not involved. These people died in the institutions where they were being housed."

At the time, because these patients were difficult to reason with, they were restrained. The difference today, she says, is the method.

"Over the years, they've used various forms of restraints. Some have been hog-tied, some have been in hobble restraints, some have had baton strikes, some have had pepper spray, and more recently now the Taser," Mash says. "What I've seen is that there's no difference from pre-Taser times to the present when Tasers are used."

For his part, however, Dawe says it's uncommon to have patients with delirium suddenly die at facilities such as St. Michael's Hospital.

All medical staff are trained how to handle patients who are acting agitated and they can usually be talked down from their state, he says.

Medical staff use a technique that includes speaking in calm tones, no matter the reaction of the patient, and neutral body language such as uncrossed arms. They try to figure out why the person is acting agitated and treat it.

Restraint is a last resort, he says.

"We believe that we are very successful in helping someone come down from an agitated place in a safe and controlled manner," Dawe says.

Dr. Peter Bieling, manager of the mood disorders program at St. Joseph's Health Care in Hamilton, Ont., said some of the responsibility rests with the police force or those who are called to deal with people with this condition.

Member of Lincolnshire (U.K.) police demonstrates Taser use. (Lincolnshire Police www.http://www.lincs.police.uk/)

"If you do know that somebody is in a vulnerable state, maybe you shouldn't use that level of force. Maybe there's something else that could be done.

"You have to conclude, and this is true for all mental illness, a person can have the disorder, but usually it doesn't fully manifest, it doesn't hit its full impact without a stressor being in place," he says.

The real challenge

Excited delirium hasn't officially made its way into the medical books yet, but Mash believes it's only a matter of time.

"It will be recognized," she says. "But these cases are rare. We're seeing more of them now for various reasons, including because people are recognizing the condition."

However, Bieling is skeptical.

"When you look at the other things that can resemble excited delirium, such as panic, hypomania, I would say that probably in most cases, those other things are likely going to be the explanation.

"If I were a betting person, I would think it's not going to make it into the next diagnostic manual," he says.

Bieling also argues that there hasn't been enough research on excited delirium to warrant classification.

"I just don't think we know," he says. "And the usual way that we figure these things out is we do studies. We do careful studies to look at prevalence."

But that's where the problem lies. Because deaths of people with these specific symptoms are rare, research in this area is automatically limited.

What's more, "what's going to make this one tough is it's so tied to a specific set of circumstances," Bieling says.

"We're not talking about something that's going to affect a huge amount of people in the general population, like depression or anxiety. What we're talking about is a specific set of circumstances when people are in police custody. That's going to make it really, really challenging."