"Things had got so bad I couldn't even remember my PIN number," he said. "My card got swallowed up twice. My memory was shot. Dosing up on smelling salts, Panadol, high caffeine sports drinks and any medical drugs like that to try and stop the dizziness, fatigue and migraines was the only way I could get through trainings and matches."
Hape said that professional rugby players in both codes frequently endangered their health by under-reporting concussion symptoms.
He hoped sharing his experiences - which he details fully in today's Weekend Herald - would help prevent young players making the same mistakes he had.
The pressures on players to play on through injuries were immense, he said.
"When you come to a new club and you are an international player you are supposed to impress. I was on one of the biggest contracts of my career [at Montpellier], so there was a load of pressure to deliver. You don't want to let anybody down. You get paid to get out there and play and you want to play. You never think [anything bad] is going to happen to you, so you do it."
He also blames the club system in the professional era.
"Players are just pieces of meat. When the meat gets too old and past its use-by date, the club just buys some more. You get meat that's bruised or damaged, the club goes and buys some more."
The brain trauma he suffered on the rugby field had damaged his personal life by affecting his ability to function as a father and husband.
"My tolerance for my three young kids was zero. I was always angry around them, couldn't even last a minute without getting cross and losing my cool. My relationship suffered."
While many of his concussion symptoms have cleared, Hape still fears for his future health.
"I can remember things that happened a long time ago but things that happened yesterday, people's names, numbers and stuff, I constantly forget. Growing up I used to wonder what was wrong with my granddad when he couldn't remember things. I'm not a granddad, I'm in my 30s. I've got the concentration span of a little kid.
"I worry about Alzheimer's and dementia. The doctors can't tell me what is going to happen to me."
Pre-season cognitive tests designed to help detect concussion were ineffective as players often manipulated the results to avoid being stood down, he said.
"Young players don't fully understand the risks of playing on with concussion. The most dangerous thing with concussion is that's its an injury you can't see. That makes it easy to ignore - something that happens far too often."
Player says he and others cheated in cognitive tests
Professional rugby players routinely manipulate the results of tests designed to stop them taking the field while concussed, says Shontayne Hape.
The former dual league and rugby international said he manipulated baseline pre-season cognitive tests and under-reported concussion symptoms during his 13-year professional career, something that was never detected by the clubs or national bodies he played for.
The admission - the first by a player of Hape's stature - comes as rugby and league authorities have been trumpeting their progress in dealing with concussion issues.
Hape said the computerised test widely used throughout the rugby world was often ineffectual - a claim backed up by a leading concussion expert.
"You have a test at the start of the season but the boys [fellow players] all know how to beat it," Hape said. "You don't do the test to your full ability. You know that when you get knocked out you are not going to be as good and that if you don't beat your score you can't come back. Everyone wants to come back, so you beat it."
Hape, who has not played since suffering severe concussion symptoms playing for Montpellier in the 2012/13 season, has retired on medical advice.
Concussion expert Rosamund Hill said senior rugby players within New Zealand had also admitted to intentionally under-performing during baseline testing.
"I have heard that from senior-level players, who I will not name, that you don't want to do too well in the pre-season testing because it doesn't give you much room if something happens," Dr Hill said.
An international player who Dr Hill evaluated at the 2011 Rugby World Cup two days after he had been knocked unconscious in a match had claimed to be free of concussion symptoms.
"He didn't look well and I didn't believe him," Dr Hill said. "The problem is you can't rely on the player in that position to be completely honest. That's understandable. It's their career. They want to play and they don't appreciate the risk to their health.
"They are understandably desperate to get back on the field. This is the pinnacle of their career. You know they are under-reporting."
Computerised baseline tests such as those employed in professional rugby and by the NRL could actually end up being counter-productive if players did not return accurate results, she said.
"It is worse than not having been tested at all because the medical professional that is looking at it is getting the wrong idea."
A foolproof neuropsychological test could be employed but it was time-consuming and expensive, so only tended to be used when players had already been diagnosed with concussion symptoms.
New Zealand Rugby insisted its concussion detection processes were robust.
"We are very confident that the processes we have in place in regard to baseline testing and in-season assessment of players safeguard against attempts to disguise concussions," medical director Dr Ian Murphy said.
Warriors doctor John Mayhew said he doubted New Zealand-based players intentionally manipulated the results of concussion tests.
"In the very old days when it was a pen and paper test the players would do that," Dr Mayhew said. "Now, if somebody tried to do that we'd suddenly have an artificial result - we'd say for a 26-year-old guy this test is crap. He might have cheated it but I'd be surprised if it wasn't picked up. The test is good enough to pick up when someone is deliberately trying to make a cock-up of it.
"We are not having the issue [Hape] is talking about. I'm not naive enough to think people don't [try to cheat the tests]. I've had people try to do that, but I think generally you'd pick up that something had gone wrong."
