Former ambulance driver Michael Kearns, 46, cut up an ambulance on its way to hospital in Chelmsford, Essex.
He pulled his car in front of the vehicle and then hit the driver, the city's crown court heard.
Kearns denied dangerous driving and assault, but was found guilty and given a nine-month suspended sentence.
Judge Patricia Lynch banned Kearns from driving for a year.
She also ordered Kearns, of Broomfield, Chelmsford, to complete unpaid community work.
The court heard he struck a glancing blow and his victim was not badly hurt.
Tom Nicholson Pratt, mitigating for Kearns, said he had suffered from post-traumatic stress after being attacked several times while working as an ambulance driver.
"He only threw one punch which connected - the driver referred to it glancing off his cheek," he said.
Kearns cared for his sick mother and worked as a driver transporting organs for transplant, he said.
Prosecutor Alex Sutter-Green told the court there was an elderly patient in the back of the vehicle and a paramedic travelling in the ambulance witnessed the attack.
"The defendant got out, opened the door and punched the victim," he said.
The court heard Kearns had a previous assault conviction following a similar incident in 2013.
Judge Lynch said: "You have led an otherwise good and industrious life.
"The post-traumatic stress from your previous work helps explain why an otherwise sensible and sane person commits offences such as this.
"It is a very serious matter and it is just not acceptable."
An organ transplant driver said to have post-traumatic stress after being assaulted at work launched a road rage attack on an ambulance driver.