Rachael Boomsma had taken a high-dose prescription Valium pill before she ploughed her four-wheel-drive into a teenager walking on the side of the road.
The 48-year-old mother left Jarrah Smith, then 16, convulsing on the side of the road as others rushed to help.
She went on to pick up her daughter from school, with her green Toyota Landcruiser showing signs of the crash.
Police found her at the school, asleep behind the wheel.
Boomsma will serve nine months in prison after pleading guilty in the County Court to one charge of dangerous driving causing serious injury and another of failing to stop.
On Friday the court heard that Jarrah was walking along Forest Drive in Mount Martha about 1pm on August 10 last year when Boomsma's 4WD left the road and crashed into him.
Jarrah was flung into the air before falling onto the side of the road.
He was put into an induced coma for 11 days while being treated in The Alfred hospital, the court heard, and was left with head injuries, a hip fracture and post-traumatic amnesia.
The court heard that after hitting Jarrah, Boomsma pulled over but did not react when a witness told her to stay where she was.
She was later found by police asleep behind the wheel outside her daughter's school. Fragments of her car were discovered at the scene.
"You must have realised you were in an accident," said County Court judge John Carmody. "Instead, you panicked and drove away without saying anything."
In a victim-impact statement, Jarrah said he had endured intensive rehabilitation since the crash and that he was having suicidal thoughts.
He said he had woken up in hospital not knowing why he was there and that his memories of overseas family holidays had been erased.
The court heard that Boomsma, who has been diagnosed with bipolar disorder, took a prescribed 10mg diazepam tablet a couple of hours before the crash to alleviate anxiety about relapsing into an alcohol addiction.
Side effects of the drug include drowsiness, slurred speech and delayed reaction. A blood test also detected quetiapine and fluoxetine in her system.
In sentencing Boomsma for dangerous driving, Judge Carmody said her behaviour was consistent with the intoxication of diazepam.
This reduced some of her moral culpability, he said, but not completely, because she should have read the medication's warning labels.
On the failure to stop charge, Judge Carmody said it would have been clear to Boomsma that she was involved in an accident and should have stayed at the scene.
After she completes her nine-month jail sentence, Boomsma will serve a two-year community corrections order. Her licence has been cancelled for four years.