Canadian rookie Lance Stroll said he felt his feet were "burning like crazy" on Friday after he had made an unscheduled stop to climb out of his Williams car during practice at the Bahrain Grand Prix.
"I don't know what it was, but there was some burning in my feet," he said. "I just had to get out of there because it was killing me -- I just wanted to get out."
Stroll completed 36 laps during the floodlit second practice session run in the evening after an earlier day-time session was held in temperatures touching 49 degrees Celsuis.
The 18-year-old, the second youngest driver in the history of the sport, was expected to stay on track to complete a Virtual Safety Car (VSC) test, but instead drove directly into the pits.
"I needed to jump out of the car, it was really, really painful," said Stroll.
"I tried to bring it to the end, but when I was told to do another lap for the virtual safety car I said 'I really cannot do it, sorry'."
He was sixth fastest in the opening session and fell to 16th in the second session.
"It was a bit of a bizarre session for me," he said.