It's been nine years since Johnson considered taking his own life while on holiday in Spain over the Christmas period in 2009.
While the TV host has continued to experience depression following the incident, he was initially reluctant to seek out a medical professional for guidance.
"I probably didn't go to see someone because I was scared of digging too deep and it getting messy," he tells The Mirror.
"It's such a shame it took me so long. I can't recommend it enough - I'd 100 per cent tell people to go and talk to an actual professional. Just do it."
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Now 36, Johnson has suffered from depression since he was in his 20s.
He explains that he thought he could deal with his depression in a "more organic way", which is why he was reluctant to see a therapist.
"For me, my life was my therapy," he says. "I've been to Thailand and chanted with monks, when I was in LA I tried yoga and meditating.
"I've done the whole 'I want to punish myself' thing too, so ran three marathons."
While Johnson thought that speaking to various people on his travels was beneficial for his mental health, finally meeting with a therapist a few months ago has made a huge difference.
He highlights the stigma that surrounds therapy, and why he thinks others suffering from similar issues may have the same reservations about going to therapy that he did.
"I have grown up in a world where therapy is for broken people and that perception is wrong," he says.
Five years ago, Johnson became an ambassador for mental health charity Mind.
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He's now working with life coach Ben Bidwell, otherwise known as The Naked Professor, on a podcast called 'The Naked Professors'.
The pair emphasise the importance of speaking openly about mental health issues, especially among men.
According to charity Campaign Against Living Miserably, 75 per cent of all suicides in the UK in 2015 were male.
"Suicide is still the biggest killer of young men, so while discussions may be happening in magazines, on TV and in the cities, I’m not sure the message is getting thought in rural parts of Wales, the valleys where I come from, for example," he says.
"My story might have been very different if I had stayed in Caerphilly."
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If you're suffering from a mental health issue and need to speak to someone, you can contact mental health charity Samaritans at their website here, email them at firstname.lastname@example.org or call at 116 123. Their phone line is open 24 hours a day and is free to use.