On Saturday, the Belgian was crowned the new Supercar Benelux Challenge with team mates Thomas Piessens and Sam Dejonghe on the TT circuit in the Assen, Netherlands.
The next day he took to the start line in the Belcar Endurance Championship when things took a turn for the worse.
"I had just taken over the wheel of our Norma prototype," said Boonen, Het Nieuwsblad reports.
"That's why I had to try to fight back past a lot of slower cars. One of those cars was the Mercedes van Heyer. He left me some space, but when I came alongside, he sent in and we met."
The pair moved towards the tyre wall, the Mercedes hurled into the air and landed on top of Boonen's Norma, just missing his head.
"I was lucky. But I don't understand how a driver can make such a judgement error with Heyer's experience."
Christophe Mallet and Dave McKenzie caught up with Tom Boonen earlier this year at the start of the 2019 Tour de France in Brussels for the Zwift Cycling Central podcast: