The former pacer, who turned 35 on Sunday, said he bullied himself into remaining normal even while he battled lows. "How have I got through to now without doing anything about it? It's different for everyone. But I think I bullied myself into doing things and trying to live 'normally'," O'Brien told 'Sunday Star Times'.
O'Brien said he first experienced depressive lows while representing his university team and continued to have the problem even while representing the national team.
"I'd just got back into the Test team after two-and-a-half years out of the mix, but for the first two weeks of our tour to South Africa, I didn't really leave my room. I was just too scared.
"I went and played cricket, went to training and did a bit of shopping. But most nights I'd eat by myself and order room service," he said, recalling the 2007 tour of South Africa.
"The rest of the time I'd either hang out in my room or sit by the pool. Wrapped up in it is how you value and see yourself. I didn't feel as though the guys I was on tour with were equals by any means. I didn't want to bother them so I looked after myself. That's still how I deal with it sometimes even now. If I'm having a few bad days, I'll try to get away from people.
"I probably should have piped up about it earlier on, just around the team and that sort of thing. But it's not easy an thing to talk about," he added.
O'Brien, who played 22 Tests and 10 ODIs taking 73 and 14 wickets respectively, joins the likes of England all-rounder Michael Yardy and former opener Marcus Trescothick in opening up about depression.
"Go back to the very start and you have to ask the question: is it cricket that acts as a catalyst for mental illnesses or is it the people who are drawn to it? I'm serious here because the sport does kick your arse very quickly. You can have a great day and then be a nobody the next.
"If you went around the dressing room, you could pick someone who was suffering from Obsessive Compulsive Disorder, you could pick someone with Asperger's Syndrome and then there's those affected by depression. There would be a small minority who would actually be quite normal," he said. O'Brien said despite the problems he has battled, he is determined to lead a normal life.
"A couple of cricketers over here, once they'd finished playing county cricket, didn't know what to do with themselves so they committed suicide. I don't want to be one of those statistics," he said.
"I don't want this to fester away either. I've never been quite that low but I've certainly been on the way to being that low. I don't want to deal with that. I don't want my wife and my daughter to deal with me like that," he added.