David Strong sat in his car, staring past the steering wheel.
"I couldn't recall if I had just driven into the garage and was meant to get out of my car, or I'd just gotten into the car and I was meant to drive out."
The next day he crashed into a cow.
"The bloody cow looked at me and wandered off. I felt like having another go at him," Mr Strong said.
These lapses were completely out of character for the 72-year-old cattle farmer and former general manager of Apple Computers, who still works roughly seven-hour days.
"When I'm driving somewhere on the farm I occasionally forget what I'm out there to do. But very quickly I can go back in my mind and think, 'ah yes, I'm going to fix that broken fence'. It comes back clearly. You can find a connection," he said.
But 10 days ago he started noticing inexplicable episodes: memory loss accompanied by double vision, poor concentration, exhaustion and a breakdown of fine motor functions. Even buttoning his shirt became a far more difficult task than it used to be.
"I'd forget what I was supposed to be doing and it was much harder to make those connections. I found it hard to go back in my mind and try to build connections from just a few minutes earlier," Mr Strong said from his room at Prince of Wales Hospital on Wednesday.
"It felt like my head was disconnected from my body; like I was operating in a haze and there was no relevance between where my head was and the surroundings," said Mr Strong, describing in remarkably vivid terms a malady that has befuddled humans for 2500 years.
Breakthrough research by Sydney researchers at the Prince of Wales Hospital and UNSW has cracked the delirium conundrum, identifying abnormal glucose metabolism in the brain as the overriding cause of the poorly understood condition.
Delirium was first described by the Greek physician Hippocrates as an inflammation of the brain (phrenitis), after noticing the condition in patients with fevers.
One in four patients over 65, and up to one in 10 patients of all ages throughout the hospital will be diagnosed with delirium, which have the potential to damage older brains even after delirium has subsided.
Doctors know how to treat the infections, illness or injuries that can trigger delirium in patients whose immune systems have been weakened by their condition.
But the root cause remained just as bewildering as a bout of the condition itself.
"It was a mystery we set out to solve," said Associate Professor Gideon Caplan, director of Geriatric Medicine at Prince of Wales Hospital.
"I felt like as a geriatrician I had a responsibility to solve the problem."
Though often seen as strictly a condition of the frail and elderly, younger adults and even children under five can develop the syndrome.
Most research in the area focused on identifying the risk factors among people who might go on to develop delirium, but Professor Caplan and his colleagues studied patients in the midst of an episode.
They used Positron Emission Tomography (PET) to scan the brains of 13 patients with a median age of 84 years old.
"We had to find people with just right level of delirium," said Professor Caplan; patients who were not excessively agitated and could lie still for the PET scan.
The scans showed "profound and widespread reductions" in cortical glucose metabolism in all delirium patients, the researchers reported in the Journal of Cerebral Blood Flow and Metabolism.
The parts of the brain that weren't properly absorbing glucose all had a direct role in delirium: the frontal lobe responsible for executive function, the temporal lobe implicated in memory, and the occipital lobe needed for vision.
"All these regions weren't lighting up on the scans," Professor Caplan said.
The scans showed glucose metabolism returned to normal once the patients' delirium had abated.
"We felt like we've cracked it. This was a unique, novel pattern.
"We were seeing something new and special. It was really 'wow', we were so excited."
The research findings offer a target for potential treatment for the source of delirium, Professor Caplan said.
He and his colleagues are preparing to trial medications - a nasal inhaler - that could increase glucose uptake in the brain and restore glucose metabolism to alleviate delirium.
Mr Strong won't need the nasal inhaler this time around - with his delirium levels largely diminished on Thursday, he'll be back on the farm dodging cows in no time.