While no-one has officially declared Vickerman's death as suicide, the terminology used by police and media suggests that was the cause.
"I think we need to use the s-word a week bit more," said Sir John. "As a precaution, people don't want to mention it, because they feel that someone who's unwell may see it as an option, but we do need to talk about it and find out why it's happening.
"It's something we need to keep working on - one of my dreams is no more suicides.
"We need to teach mental health in the schools. We teach them maths and science, but not that things might not go to plan and you need to have your mental health in order."
Sir John warned that sportspeople were particularly vulnerable, given their often single-minded pursuit of perfection.
"I think the percentage in NZ is one in five will suffer from mental illness in their time. Sometimes sportspeople can be a little bit more susceptible, especially when they finish, because the lights go down and the phone stops ringing.
"Most of our peers have 10-12 years of a rugby career and then have to start again. Then, it doesn't matter how much money you have in the bank, it's more about where you're at.
"There's a huge percentage in American football that, five years after they've finished, they're broke, divorced and have some sort of mental health issue ... and they earn a million dollars a year.
"I think the pressure on young people to succeed in professional sport is a very, very difficult time and we're quite obsessive by nature. We're very committed to one thing and you have to be to make it, so there are some tendencies in our sport that make us susceptible to mental health issues."
Sir John made it through by treating his illness like a sports injury.
"I went to a specialist and told her I was a rugby player. She asked what I would do with a tight hamstring, and I said I'd stop and stretch it.
"If it was still tight, I'd ice it and go see a physio. She said the brain was no different and that put it in a simple way for me - I thought 'I've got a hamstring in my head'.
"I put some ice on it, which at the time meant taking some medication that helped bring some balance back in my life, and went to the physio, which was called a psychiatrist. I started on my journey of wellness."
The key for Sir John was finding activities that helped him relax. For him, that meant reading, cooking and exercise.
"My message is go on a journey of wellness," he told Devlin. "What do you do each day that will reboot you?"
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• Samaritans 0800 726 666
• If it is an emergency and you feel like you or someone else is at risk, call 111.
