Glasgow Sheriff Court has previously heard that Harry Clarke was unconscious at the wheel when the lorry hit pedestrians on 22 December last year.
First Bus inspector John Stewart told the FAI that Mr Clarke had blacked out while unwell at a bus stop in 2010.
The inquiry is examining the bin lorry, its route and Mr Clarke's health.
Mr Stewart told the second day of the FAI, which is being overseen by Sheriff John Beckett QC, that he was an inspector and had been with First Bus Glasgow for 12 years.
He referred to notes he had taken on a Blackberry, detailing an incident involving Mr Clarke, while he was a bus driver, on 7 April 2010.
The notes of his daily report from that day state Mr Clarke "blacked out for a couple of minutes" while at a bus stop having "taken unwell".
Mr Stewart said he was alerted by a passenger on the number 54 bus that the driver had collapsed at the wheel.
The witness said Mr Clarke was still in the driver's seat of the bus when he arrived at the scene, but there were no passengers on board.
An ambulance was called and paramedics arrived to attend to Mr Clarke who was given the all clear and refused to go to hospital.
He was not allowed to drive the bus back, which was returned to the depot by Mr Stewart.
The witness said his involvement ended as soon as he left Mr Clarke and that he assumed the driver would have been sent to the company doctor.
Mr Stewart, under cross-examination from Dorothy Bain QC, agreed that "other people could be killed" due to a driver being "out of control" of the bus.
The witness said he did not know if a driver who had blacked out would be suspended, but he said he would not let them drive.
Going back over Mr Stewart's report, it was noted that Mr Clarke had driven the bus to the stop he was at after blacking out.
Mr Stewart said Mr Clarke "should have used his common sense" and not driven the bus, but said "you would have to ask him".
Ms Bain asked Mr Stewart if knew that Mr Clarke was suspended from driving and had to attend doctor's appointments. The witness said he did not.
The court was then shown a letter from a First Bus doctor saying Mr Clarke had suffered "loss of consciousness".
In a letter, the doctor said Mr Clarke was advised that "he does not need to inform the DVLA of the incident".
Ms Bain asked Mr Stewart if he knew Mr Clarke had reported passing out in a canteen at work that same day in 2010. The witness said he did not know.
Mr Stewart said he could not confirm if Mr Clarke had been suffering from dizzy spells, but said he would have stopped him driving if he had.
Mr Stewart will give evidence on Friday when the FAI resumes for a third day.
Earlier, the inquiry heard again from Henry Toal, who was a member of the three-man crew of the bin lorry on the day of the crash.
He told the inquiry on Wednesday that he was not aware of Mr Clarke having any serious medical condition and would have reported any issue.
On Thursday, Mr Toal told the court that the first he knew of any problem on board the lorry was when his fellow crewman, Matthew Telford, asked Mr Clarke what he was doing.
The witness said Mr Clarke was slumped over to the left side and "didn't look conscious".
Mr Toal recalled that Mr Telford loosened his seatbelt, leaned forward and hit Mr Clarke in the back but there was no response from the driver.
He said Mr Telford was shouting, "Harry, you're killing people", but he could not remember if he shouted anything himself.
The witness told the court that he was "terrified" and thought they had initially hit poles and bins on the left-hand side of the truck.
He then recalled that the lorry "hit a few people" and a taxi before hitting the wall of the Millennium Hotel.
Mr Toal said he kept his seatbelt on and pushed himself into the wall of the cab as it sped along Queen Street and could not remember doing anything.
He said he suffered a "burst eye" in the incident.
Solicitor General Lesley Thomson, Scotland's second most senior law officer, who is leading the FAI, read from a police statement the day after the crash in which Mr Toal said Mr Clarke's hands were on the wheel.
Mr Toal said "it was a long time ago" but agreed that Mr Clarke's hands were on wheel, but he may not have been gripping it.
The issue of unopened beer bottles in the lorry cabin, which Mr Telford denied having any knowledge of during Wednesday's evidence, was raised again.
The witness said he only learned about the beer bottles the day after the crash when asked by police.
Mr Toal agreed that bin lorry crews were sometimes given gifts, such as alcohol, at Christmas but said he did not remember any given on the day of the crash.
While being cross-examined by Alastair Forsyth QC, for Gillian Ewing's family, Mr Toal agreed that accepting gifts or bringing beer on to the lorry would constitute misconduct.
Questioned about the handbrake, the witness said it never crossed his mind that he could have tried to engage it as he could not have reached it.
The court also heard from Glasgow City Council employees, Alan Kernaghan and Ian Quigley, who are both bin lorry drivers of significant experience.
Both men told the court they had seen Mr Clarke on the day of the crash and had no concerns for his health of ability to do his job.
The court was told of some procedural changes to bin lorry collections following the crash, such as shorter routes and smaller vehicles for the city centre and pedestrianised areas.
The court also heard that Mr Clarke had since returned to work since the tragedy, although not on driving duties.
The first day of the inquiry heard from Mr Toal's fellow crewman, Mr Telford.
The inquiry, which is expected to run for several weeks will examine the medical background, employment record and training of the driver, Mr Clarke.
It will also look at technical aspects of the vehicle and whether any measures could have brought it to a controlled stop, and the safety of the route taken by the vehicle given the time of day and year.
Erin McQuade, 18, her grandparents Jack Sweeney, 68, and his 69-year-old wife Lorraine, all from Dumbarton, died in the incident in the city's Queen Street and George Square.
Stephenie Tait, 29, and Jacqueline Morton, 51, both from Glasgow, and Gillian Ewing, 52, from Edinburgh, were also killed when the truck mounted the pavement before crashing into the side of the Millennium Hotel.
A further 15 people were injured.
The Crown Office has already concluded that there will be no criminal prosecution over the crash, with senior lawyers deeming it a "tragic accident".
The fatal accident inquiry (FAI) into the Glasgow bin lorry crash which killed six people has heard the driver blacked out before while driving a bus.