Ronnie O'Sullivan has revealed that he "lost himself" for seven years to alcohol and drugs, and came to learn that "happiness is an inside job".
O'Sullivan has had well-documented issues with drink, drugs and depression.
He was stripped of the Irish Masters title in 1998 after testing positive for cannabis, and in 2000 entered rehab to treat his addictions.
"There are massive gaps," the 47-year-old told BBC Radio 4 Today.
"I lost six, seven years to drinking and taking cannabis. Then four years of dealing with stuff away from the table which I didn't deal with very well.
"I wasn't focusing on snooker. But I suppose everyone has those problems, but there's 10 years there where I didn't really do much. I didn't practise much, I didn't have the headspace to win."
The current world number was knocked out in the quarter-finals of this year's World Championship tournament by eventual champion Luca Brecel.
During his lowest points, O'Sullivan - whose parents were sent to prison during his teenage years - said he relied on alcohol and cannabis to "get through the day".
"I lost my personality and confidence and needed to take substances just to feel like I could socialise," said O'Sullivan, whose latest book Unbreakable was released on Thursday.
"Then you get clean, and you become awkward in social situations and you think 'how do I deal with these situations?' You get a bit anxious and it started to affect me in certain ways. How do I live clean?
"It was weird - I had to learn to do all that stuff again. It took time but once I got there, I realised you have to carve out a different life for yourself. Maybe I'm not suited for X, Y and Z.
"My happy place is going running in the morning and I go out with my running friends, and I'm cool with that. Put me in an environment where there's lots of people and I run for the corner."
However, O'Sullivan now views the game as "great escapism", with snooker halls the place he goes to "feel relaxed and calm".
"I always loved my sport and that's what's most important to me. That strips away any temptations of going out," he said.
"I think going to rehab taught me happiness is an inside job, which I truly believe. So since that moment in 2000, I've always believed that."
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