Osher added that because of his thinking compulsion, his body would react to those patterns.
"I would see, not imagine, but see the ocean inundating the houses, the buildings and the people," he said.
"Every thought coming through is so painful, I flinch as if it's pain. I created the most awful thing that could ever be imagined and I would see it in everything."
"If I turned the air conditioner on, it meant that climate change would destroy the world and it was like every three to five seconds. It got to the point where after a few hours of that you're like 'This can't stop and I can't stop it.'"
The Bachelor host added that knowing that his thoughts were irrational was what made it the most "painful."
"I absolutely realised it was irrational and crazy, and yet I couldn't stop it."
Osher also referred to his wife of four years Audrey Griffen, a make up artist whom he met on the set of The Bachelor season two and how his disorder affected their relationship.
"Audrey early on was able to see the difference in me and my sick brain and thankfully she fell in love with me."
In the episode, Osher also shared his darkest moment dealing with OCD including when he was prepared to take his own life.
"I had in the past been at the point where I hadn't left the house for three to five days at a time. I was still drinking and using back then so it was just a never ending pit of day drinking, compulsive internet gambling and compulsive masturbation."
He went on to say that at a point he found himself in so much pain that he would've "absolutely done anything" and thought about ways to "make it stop permanently."
"It was the best idea I'd ever had, the kindest thing I could've done for myself and everyone around me. The seductive way that those thoughts came into my head, I was so lucky to know 'Holy s*** if that has suddenly become a good idea, maybe that's as distorted as all the other stuff I'm seeing.'"
"If you know my story, you'll know that I have a different brain. One of the things I get to have which makes me very good at my job is OCD. Sometimes though - it's been really, really horrible," he wrote.
"According to @saneaustralia, roughly 1 in 50 Australians have Obsessive Compulsive Disorder (OCD). However, of all mental illnesses, OCD remains one of the most misunderstood.
"People with OCD are plagued by excessive, intrusive, and often highly distressing thoughts (obsessions) that can lead to repetitive behaviours (compulsions) aimed at relieving those thoughts."
He added: "I'm a lot better now thanks to some great meds and some greater doctors who guided me through exposure therapy - but it's something that my brain just does.
"Watching the episode about OCD and seeing other people describe things that I thought only I felt is such a sense of relief. And I guess that's what it's all about. Knowing you're not alone."
Fans praised Osher for sharing his story and speaking up about the mental health condition.
"I appreciate you for always using your voice and your platform to talk about important issues that are not discussed enough. Thank you," one wrote.
"This was a great episode.. thanks for opening up about your OCD," another penned.
"Just reading this post hits close so thank you for helping to make the voice heard but more importantly for helping those of us with ocd. Sometimes just hearing other stories is such therapy," a third mused.
If you have been affected by any of the issues in this article, help is available. Visit the Lifeline website or call them on 13 11 14