"I locked eyes with my dad and I realised that was it, I was going over."
Dylan doesn't remember plummeting to the ground, only hitting the rocks below with such force he blew through the soles of his shoes, ripped open his jeans and fractured his calf bone.
"I just remember that first initial impact," he recalled.
"Somehow I got my feet underneath me and that absorbed most of my shock."
He fell back onto rocks, which chipped his vertebra.
Dylan thinks his backpack, which contained a rolled up towel and shirt, saved his back from further damage.
Rushing to his son's side, Donald tried to make the 20-year-old comfortable before running the 1km back towards his friend's bach for help.
They set off an emergency locator beacon and 50 minutes later Auckland's Westpac Rescue Helicopter landed nearby.
Dylan was flown to hospital and discharged the next day.
Months of rehabilitation and assisted living followed. Nearly six months on, Dylan considers himself fully recovered, the only reminders a few scars and slight nerve damage to his leg and back.
"It's a miracle. I don't know how you could survive the fall with only a fractured leg," Donald said.
"But he wouldn't have survived if Westpac didn't make it as fast as they did, because he was in serious shock and panic. He thought he was going to die."
The Holzheimers praised the helicopter staff, saying their speed and support in that crucial time period was invaluable.
"The crew were amazing, they really helped let me know everything was going to be alright and I was in good hands now," Dylan said.
"They took really good care of me."
The family were now regular donors to the Auckland Westpac Rescue Helicopter trust and have had the chance to meet the crew in person, thanking them for their efforts.
"We had a chance to sit with him for about an hour, and they're good people," Donald said.
"It's just amazing to talk to people like that who are willing to do these things."
"I can't emphasise enough how you hope you won't need this service, but the day you do need it you hope it can get there [in time]," he said.
"Especially in New Zealand there's a lot of remote places, a lot of dangerous terrain."
Dylan said the experience taught him to value how he spent his time, and has since started a fishing youth group, which functions like a big brother programme.
Auckland's Westpac Rescue Helicopter service needs your support for their 2017 Summer Appeal. December 2016 was the busiest month on record for the charity, with 126 rescue missions. Please visit rescuehelicopter.org.nz if you would like to gift a donation or call Freephone 0800 4 RESCUE (0800 4 737 283).