Steven Anthony McGregor will spend at least two-and-a-half years behind bars for the drug-fuelled crash on the New England Highway, at Deepwater in 2016.

The court heard McGregor made an admission to a specialist doctor about falling asleep at the wheel.

He pleaded guilty in November, last year, to dangerous driving occasioning death while under the influence, and was given a discount of 15 per cent for the timing of the plea, before any trial.

McGregor was headed towards Queensland on the highway when he fell asleep at the wheel, about 32km north of Glen Innes.

His mother, Patricia, was a passenger in the front seat of the 2002 Ford Falcon when he ran off the road and struck a tree about 5am. Mrs McGregor was trapped and “died as a result of her injuries”.

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The court heard about 10pm the night before McGregor had been taken to Tamworth hospital for a mental health assessment, after police were called to reports of McGregor damaging a National Australia Bank ATM in Tamworth.

He was released shortly after 1am on September 2 and headed off on the trip.

McGregor’s blood and urine samples taken while he was in hospital for his injuries after the crash, showed traces of drugs including amphetamine and methylamphetamine.

A specialist report showed McGregor was “under the influence of methylamphetamine” and the levels showed there “would have been significant impairment of his driving ability", Judge McLennan detailed in sentencing.

The court heard McGregor “recalled seeing a straight road … and his mother saying ‘son, son’” before the crash impact.

“[McGregor] drove in a sleep-deprived state under the influence of a drug,” Judge Jeffery McLennan said, adding he was under the “influence of the drug described as significant".

Judge McLennan said the 37-year-old’s criminal history showed significant matters on his record from Victoria including recklessly causing serious injury, burglary and fail to stop after an accident.

“The offender has been reckless towards the life and safety of others ... for a significant time,” he said, adding the death of his mother is "one more tragic example of this type of conduct".

Following two victim impact statements from McGregor’s siblings, Judge McLennan said it was clear the harm that had been inflicted on the family.

“They too have lost their cherished mother, and their retrospective victim impact statements make for poignant reading,” he said.

“No term of imprisonment will make up for that loss.”

McGregor was jailed for two-years-and-six-months with an additional 18 months on parole. He’ll be eligible for release in March, 2020.