Robbie Price was cycling to work when he slammed head first into a traffic sign and "woke up in someone else's life".
The accident last Monday caused severe amnesia, costing the Hamilton scientist the past 10 years of his life.
The 43-year-old didn't know he and his family had moved here from Australia in 2002 and can't remember anything since then, including the childhood of his two teenage sons, who he thought were aged 5 and 3.
Mr Price can't go back to work yet because he doesn't remember how to do his job at the Landcare Research crown institute, where he carried out environmental research as part of a programming group. At least, that's what he's been told.
"Things are really confused. But the doctors assure me that I'll wake up one morning and it will just be normal."
Many of the blanks of what happened on the morning of the accident have been filled in by his wife, Roshni Kanta, while the couple await the police report.
However, a witness says Mr Price was cycling over a rail bridge in Frankton when he hit a road sign temporarily placed in a cycle lane.
Mr Price - who didn't realise he was chairman of the Cycle Action Network Waikato until he stumbled upon that fact while using a computer the other day - thinks he must have been travelling at up to 50 km/h.
With no visible injuries, he was taken by ambulance to an accident and emergency clinic where he fell asleep, slipped into a concussion and suffered the amnesia.
When he came to, he didn't know where he was, and didn't recognise his $8000 mountain bike.
"That was confusing because the bike in the room wasn't mine. It was mine, but by then I'd lost 10 years of memory so I was expecting if I'd had a bike accident the bike should be my old bike.
"The next bit I remember quite well ... going to the bike and opening it up and finding a wallet with a New Zealand driving licence. It was at that point I completely lost it. I can remember being just completely freaked out because you've woken up in somebody else's life.
"Looking back at it now, 'two hours ago' I had been riding in the middle of the countryside in New South Wales."
Despite the presence of his wife, Mr Price became emotionally erratic, laughing one minute and crying the next.
He was taken by ambulance to Waikato Hospital, where doctors told him his brain was bruised and it could take between 2-3 days and 2-3 years for all of his memories to come back.
They recommended "no thinking about work" for six days, not to meet many people, and getting plenty of rest - including no cycling for a month, to protect his head.
In the meantime, Mr Price has to hear bad news all over again, such as the death of close relatives and that his father is ill.
He's trying to catch up on world events, including the Christchurch earthquakes, the fact the US has its first African-American President, and the number of wars happening.
Passwords, bank account numbers and eftpos PINs have not been easy, and being reintroduced to old colleagues has been disconcerting.
"I spent the first few days looking up words in the dictionary," he said.
Even old technology such as mobile phones felt foreign to Mr Price, who had to relearn many of the functions.
Strangely, he remembers clearly events before 2002, and a cycling accident he had in Australia is as vivid as the day it happened, because for him it feels like only a few weeks ago.
Fortunately, he can form new memories and his short-term memory is intact.
Mr Price was optimistic his memory would return slowly.
He said it was "too depressing" to think he might not get back the memory of his children growing up. "It's temporarily misplaced. It's not lost."
Ms Kanta was philosophical about the accident - she has been there to help her husband recover from several cycling mishaps during their 18-year marriage. "He's normal, he will get better," she said.
GP Leo Revell confirmed Mr Price was being treated for amnesia, which appeared to be severe.
A University of Auckland neuro-psychologist, Associate Professor Lynette Tippett, said retrograde amnesia following a head injury usually involved losing memories of only a short period of time, but much longer periods were not impossible.
Professor Tippett said retrograde amnesia typically disrupted memories of the trauma event and the hours or days before.
"The most recent memories are less well consolidated in the brain and are more vulnerable to disruption.
"What that means is the most recently formed memories are more likely to be disrupted by damage to the memory circuitry than memories from way back in time."
Dr Phil Wood of The Memory Clinic in Auckland said memory was a vulnerable and actively dependent part of brain function.
The geriatrician, who deals with dementia in elderly patients, said most retrograde amnesia diminished and the memory was reconstructed from other sources over time.
He recommended that amnesia sufferers use photos and stories to help retrieve memories.
"What you're lacking is the hooks to pull the information out and sometimes just that ability to trigger a memory is what it takes."
Mr Price will be reassessed by his clinic in another two weeks to determine if he needs specialist treatment.
What Robbie Price can't remember
March 2003: The United States invades Iraq.
December 2004: A 9.1 magnitude earthquake off Indonesia and ensuing tsunami kill 230,000 people.
August 2005: Hurricane Katrina hits southern coast of the United States, killing 1800 people and causing US$81 billion worth of damage.
April 2007: 32 people killed in Virginia Tech University massacre in United States.
December 2007: Most of developed world enters a financial recession.
January 2008: Sir Edmund Hillary dies.
November 2008: Barack Obama elected first black President of the United States.
June 2009: Michael Jackson dies.
February 2011: Magnitude 6.3 earthquake strikes Christchurch, killing 185 people.
March 2011: Magnitude 8.9 earthquake off the coast of Japan triggers a giant tsunami which kills 15,854 people.
February 2012: Whitney Houston dies.
Technology that didn't exist before 2002: