The singer served an eight-week sentence and was fined after driving into a photo shop.
In an interview with BBC Radio 2 that is set to be broadcast Monday and Tuesday, Michael said, "This was a hugely shameful thing to have done repeatedly," referring to a history that includes a previous drugged-driving arrest.
"Karmically I felt like I had a bill to pay. I went to prison, I paid my bill."
He called himself "the poster boy for cannabis" and said he is seeking treatment.
Michael said his time in London's Pentonville prison was not so bad, since "it's so much easier to take any form of punishment if you believe you actually deserve it, and I did."
He later was transferred to the Highpoint open prison in Suffolk, where he signed a guitar on his last night and was asked to put the date on it.
"The guy said it's the 10th of the 10th of the 10th. And I just thought, 'That's so fitting.' It's like the clock rolling round to the end of something. Tomorrow I start again."