The 29-year-old revealed to Carrie Bickmore that he initially thought he was suffering from depression before learning that it was actually a malignant brain tumour.
"I'd even gone to the doctor and the doctor said, 'You know, all the symptoms seem like depression."
But after finding out he had a brain tumour, Johnny's neurosurgeon told him it was just the immense pressure on the brain.
"After having found the tumour, the neurosurgeon said, 'No, no it's not depression at all, it was because there was so much pressure put on your brain, it was causing all these different symptoms."
When Carrie asked how long the tumor had been growing, Johnny replied: "The surgeon said it could have been potentially growing from two to ten years."
Telling all, the actor also revealed his long-term girlfriend Tahnee Sims was the one asked by doctors to sign off on his brain tumor operation and was told her was 1/20 chance he'd not make it through.
Now undergoing regular chemotherapy and radiation sessions, the star who's on the road to recovery has made it no secret how appreciative he is of the medial staff that continue to help him.
The former Home And Away actor also said that he was later told by doctor's that he would have died that night with a brain aneurysm if he didn't go to emergency for what he thought was a migraine when he did.
"It's sheer luck I went in when I did and everything happened the way it did or I wouldn't be here," he told Carrie.
This article originally appeared on New Idea.