Mitchell's lawyer, Fiona Guy-Kidd, described it as a ''lapse of judgment'' and said her client had done everything he could to ''make it better''.
That included paying the insurance excess, reimbursing the owner of the other vehicle for petrol and making an emotional harm payment.
Judge Brandts-Giesen described it as ''pretty bad driving'', but Guy-Kidd said Mitchell had ''no recollection of it''.
''He doesn't know if he was awake at the time.''
The judge responded: ''Sleep-walking is an interesting conclusion''.
''There are plenty of people, in particular children, who may sleep walk, but not many of them go driving vehicles.''
Guy-Kidd said a letter from his mother, provided to the court, indicated there was ''further activity than just walking'', exacerbated when he was ''very tired''.
However, Judge Brandts-Giesen told Mitchell to discuss the potential medical condition with a doctor.
''Claims like this may be valid, but it may be something to be managed in another way.
''Alcohol is not a good way to manage sleep-walking.''
Judge Brandts-Giesen said alcohol ''clearly'' played too great a part in Mitchell's life and ''gets you into trouble''.
He accepted his two previous convictions for drink-driving were ''some years'' ago, but Mitchell should have ''remembered and would have learned something'' from them.
''You seem to have a bit of a wild south attitude towards drinking and driving. All too often [that] results in shattered lives and battered cars.''
Mitchell was disqualified for 15 months on both charges, backdated to September 26, 2017, sentenced to nine months' supervision with special conditions, and ordered to complete 150 hours' community work.
