Mr Rook then reacted, over-corrected and crossed the centre-line, smashing into the oncoming Subaru driven by 20-year-old Finlay William Dunning.
Mr Dunning died at the scene.
Mr Rook pleaded guilty to careless driving charge causing death.
Defence counsel James Rapley told the court that there was no speed or recklessness involved.
The error by Mr Rook came by not taking enough breaks, he said.
Mr Dunning was a young man taken from his family, and Mr Rook is "very much aware of that - it's something we've talked about it a lot", the lawyer said.
Mr Rook, a well-regarded worker at a local firm involved in the city's rebuild, wrote to Mr Dunning's parents expressing his remorse but they understandably did not want to receive the letter, Mr Rapley said.
Judge Paul Kellar said careless driving causing death cases were the "most difficult" he has to deal with in the district courts, in terms of the necessary legal and moral judgements involved, along with the "very human factor".
The case involved the death of a "much-loved, upstanding young man" caused by the careless inattention of another equally much-loved and upstanding young man.
There is a "terrible irony" that both Mr Rook and Mr Dunning were much the same age, the judge noted.
Judge Kellar said that given the action-packed weekend, and the long trip back, Mr Rook should've have been aware of the need to either take more breaks or rest, or else share the driving with his friends.
He sentenced Mr Rook to 125 hours of community work and ordered him to pay $10,000 of emotional harm reparation as a "token" to the Dunning family to "do with it what they will", possibly donate to Spirit of Adventure which Mr Dunning so loved.
Mr Rook was also disqualified from driving for nine months.