"There was an outside reality and an inside reality when it came to who I was," he said.
"On the outside, I was very privileged and very fortunate, born and raised in Mosman. I went to a good school, did well in my HSC, hung out with the cool kids and had a girlfriend. I went to Sydney University to study commerce, I was the youngest Microsoft intern in Australia and went to the US.
"My job was incredible. I met with Robert Downey Jr one-on-one in Hollywood and flew to Milan to meet with Vogue at Design Week because that was my job. I flew business class and drove a Porsche. You name it, it was the Instagram moment. But the internal reality was so totally plagued with anxiety 24-7."
Last year New Zealand's annual provisional suicide number was the highest since records began, rising for the fourth consecutive year to a record 668 deaths.
New Zealand's suicide rate – the number of suicides per 100,000 population - is now over 13 for the first time. It has been recorded as 13.67, up from 12.64.
And research shows men are significantly less likely to reach out for help when they're struggling.
Wallis had struggled with obsessive-compulsive disorder and anxiety since he was a child but managed to find a way to push that turmoil down.
By his mid-20s, Wallis was struggling with crippling anxiety and depression despite seeming to have the perfect life.
"The reason I'm still here is because I found this guy's story," he recalled.
"He was in his bedroom and recorded a video on his webcam. I found it on YouTube on one of my darkest days when I didn't really know if I was going to live.
"It was the first time in my life I felt understood. I realised that's what I'd been craving all my life. Not for someone to take the problem away but just to know that someone got it, that it's OK and I'm enough.
"It was huge to feel understood and like I didn't need to reinvent my life but simply pivot my perspective. It puts words around sensations and experiences and thoughts that I'd had."
Hearing someone make sense of all the things that had plagued him for years, which he thought made him broken or crazy and he'd never been able to put into words, was like being freed from jail, he said.
He walked the streets of Seattle, where he was living and working for one of the biggest companies in the world, and sobbed.
And so, Wallis quit his job and returned home to Australia.
"One day, no job and no nothing, back in my parents' house in Mosman, I went down to the beach and asked a friend to record a video of my story, just like that guy had," he said.
"I figured if one person felt understood, like I had, then it could be the spark of a journey for them. It might give them permission to accept the things that cause them pain.
"I drew a heart on my arm and said that I wanted to wear my heart on my sleeve."
Within a month, his movement was born. People began recording and sharing their own personal stories on the platform, drawing hearts on their arms like he had.
"To my amazement, people even started tattooing hearts on their arms too, like I had," Wallis said.
"In two years, it's one of the fastest-growing movements and is the platform on the internet if you want to tell your story or, better yet, to hear other people's stories.
"It's kind of a symbol of the Millennial generation — I'm in charge of who I am and I want to live a life of authenticity. It shows that I want to remove the mask and be real.
"The reason why it resonated so much is because it's a shift from the questions like 'are you OK?' towards 'I'm not OK'. It's a shift away from waiting for people to ask and waiting for everyone to check in to putting your hand up."
Like many men, Wallis said he struggled to reconcile what he was feeling and wasn't confident to talk to his loved ones about it.
Working in the mental health space, he's acutely aware of the men's mental health crisis.
"It's interesting because females and males are actually as likely to suffer from mental health issues. It's a pretty equal split. The difference comes with suicide.
"Men are so much more likely to die by suicide. What that says is the incidences of pain are the same, but the way we think we need to deal with it is different.
"For guys, we're not having earlier conversations, and we're jumping towards the end of the path straight away. The only way out is the black-and-white life or death versus something being in between. I think women see the grey more than men can.
"Men look for certainty in their solutions, I think.
"We need to redefine what vulnerability and strength is. Vulnerability is strength. We need role models, almost really hyper-masculine role models, to show that you can be tough and be real."
Wallis found a therapist he could connect with, began taking medication and changed his lifestyle so it was more conducive to wellbeing.
But a big part of the success of his recovery was changing his "internal narrative", he said.
"I didn't know who I was, and from a young age, I'd been carrying a series of narratives with me about myself - I'm a bad person, I'm crazy, no one can help me. It all got too much.
"Therapy, medication … all those things are tangible, for sure, but the reality is that if you have a toxic narrative inside your body about who you are, no amount of yoga or meditation or therapy is going to help. You have to make peace with who you are first.
"Before you go and change anything, you have to feel like you're enough as you are right now. Then, on top of that, intervene with meditation, yoga, medication and therapy because all of those things are valid. But you've got to accept yourself first."
The stream of personal stories from around the world still flows, but Heart on My Sleeve has now evolved into a service provider organisation.
"We've created a 10-hour online learning course that we'll also roll out in half-day corporate workshops," Wallis said.
"It teaches people how to find their voice, how to speak up, how to support others in a new way, how leaders and managers can talk to their employees with confidence."
Where you can get help:
If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call 111.
If you need to talk to someone, the following free helplines operate 24/7:
DEPRESSION HELPLINE: 0800 111 757
LIFELINE: 0800 543 354
SAMARITANS: 0800 726 666
YOUTHLINE: 0800 376 633 or text 234
1737 NEED TO TALK? Call or text 1737
