Fraser Watt spent more than a month in intensive care after his car collided with the farming vehicle on a road between St Andrews and Dundee in 1983.
Medics rushed to save Mr Watt following the incident, however the injuries he sustained resulted in him losing almost a quarter of his brain.
But Mr Watt, who was 24 at the time of the crash, astonished doctors when he awoke from his unconscious state and began conversing in Malay – the language he spoke as a child while growing up in Borneo.
Now 60, he spoke of the frightening incident at the opening of a new base for brain injury charity the Edinburgh Headway group in the Capital on Wednesday.
The organisation aims to “empower and enrich the lives of adults who have survived an acquired brain injury” through a programme of rehabilitation.
Mr Watt lived in Borneo with his civil engineer father and spent a lot of time with the family’s cook, meaning he became fluent in Chinese and Malaysian by the age of five.
But family members were shocked when he woke up communicating in a language he had not spoken for almost 20 years.
He said: “Everyone was stunned when I spoke Malaysian – so was I because although I was fluent as a child I hadn’t spoken Malaysian for 19 years before the crash.
“My mum was at my bedside so she could translate for the doctors until the end of the day when my English returned.”
Mr Watt returned to Scotland in the 1970s and later gained a degree in chemistry and biology at Abertay University.
He was driving home when the tractor pulled out in front of him and despite wearing a seatbelt at the time of the crash, broke through the windscreen and suffered serious injuries.
It is understood the tractor driver who caused the crash received three points on his licence after driving on a provisional licence with no L-plates and faulty brakes on the trailer.
However, the life-changing injuries to the front and back of Fraser’s brain resulted in several years of recovery, forcing him to learn how to walk again.
Mr Watt added that he still feels painful, migraine-like headaches on a daily basis, more than 30 years after the crash.
He said: “My memory is now permanently scrambled but every so often an isolated memory comes to the surface for me to see.
“The biggest struggle though is because I look fine on the surface people assume I’m stupid or they just don’t have the patience while I struggle to recall memories or articulate thoughts.”
Mr Watt added: “Other than that, I’ve learned how strong I really am and how to survive whatever comes my way.”