The ARIA Award-winner was charged with high-range drink-driving after the collision on Wednesday night.
Johns later said in an Instagram post he had been struggling with panic attacks and mental health issues and would be going to a rehabilitation facility.
"I've been self-medicating with alcohol to deal with my PTSD, anxiety and depression," he wrote.
"I know this is not sustainable or healthy."
NSW Police said a grey SUV drove out of a service station on the Pacific Highway at North Arm Cove about 10.30pm on Wednesday.
A short time later, the northbound SUV collided with the southbound van after the SUV moved onto the wrong side of the road.
Both vehicles ended up on a nature strip.
Paramedics assessed Johns, 42, at the scene and he returned a positive roadside breath test to police.
He was later allegedly returned a second breath test of 0.157, more than three times the legal limit.
The van driver, 51, and his female passenger, 55, were treated at the scene and the passenger was taken to John Hunter Hospital before being released.
Johns said his "mental health is a work in progress" and "it's something I always have to manage".
"Over the past week I began to experience panic attacks," he wrote on Instagram on Thursday.
"Last night I got lost while driving and I was in an accident. I am ok, everyone is ok.
"I have to step back now as I'm self admitting a rehabilitation center and I don't know how long I'll be there.
"Appreciate your love and support as always."
Johns will appear in Raymond Terrace Local Court on April 11.
