William Swale, 69, spoke publicly for the first time on Tuesday as he gave evidence on the first day of an inquest into the deadly 2023 crash in Daylesford, regional Victoria.
He originally objected to giving evidence, but was compelled to do so by a coroner in December.
Mr Swale suffered a severe hypoglycaemic episode as he drove home from a clay shooting event, mounted a kerb and drove into people sitting outside the Royal Daylesford Hotel.
Pratibha Sharma, 44, her daughter Anvi, 9, and partner Jatin Kumar, 30, their friend Vivek Bhatia, 38, and his son Vihaan, 11, were killed, and six others injured.
Mr Swale was initially charged with 14 offences, including five counts of culpable driving causing death.Â
But all charges were struck out by a magistrate who found his actions were involuntary.
Mr Swale said he hoped the families of those who died might be in court on Tuesday, as he offered an apology.
"This was an incomprehensible tragedy, a catastrophe, you could say an unfortunate series of events, and I acknowledge that I will have traumatised the families enormously," he told the Coroners Court in Melbourne.
"I think of them from the moment I wake up, to the moment I go to sleep.
"I am certainly so sorry to the families. I was a catastrophe which should not have happened, I'm devastated that I was even part of it."
He described thinking it was dark and feeling vague in the hour before the crash, which occurred about 6.07pm on November 5, 2023.
Mr Swale said he ate a shepherd's pie for lunch and took six units of insulin, before leaving a clay shooting event feeling "extremely elated".
He said he left Clunes about 4pm and had to get his car jump-started because of a flat battery.
Before leaving he checked his glucose monitoring device, connected via an app on his phone, which recorded 7.2mmol/L at 3.58pm.
By 5.17pm he had a reading of 2.9mmol/L, signalling he was becoming severely hypoglycaemic.
Mr Swale said at this time he stopped in Daylesford and entered the Winespeake Cellar + Deli to get food, but was turned away because they were busy.
He then made "very stupid decisions" in not trying to source food, as he described his brain shutting down because of hypoglycaemia.
"I have a very good memory of making very stupid decisions, like Alice in Wonderland," he said, giving examples including not getting takeaway food from the deli and not eating fruit and nuts he had inside his car.
He remembered little else until he was with paramedics at the scene after the crash, as he had blacked out.
Coroner Dimitra Dubrow is investigating awareness, education, management of diabetic drivers, and laws around outdoor dining.
Mr Swale said he recalled engaging in a diabetes training course in 1994, when he was diagnosed with type-1 diabetes, but could not remember if it involved information on driving awareness.
He had not received any formal training on driving with diabetes in the three decades since, but would have had conversations with his endocrinologist about this, he said.
This included discussions on how to use his glucose device, which Mr Nathwani said registered 10 alarms for low levels before the crash.
Mr Swale said he did not hear alarms, blaming issues with his phone connecting to his car via bluetooth.
He said he did not know drivers needed to notify VicRoads if they were diabetic until he sought a truck driving licence about five years ago.
The inquest continues on Wednesday when Mr Swale's endocrinologist will give evidence.
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