Alpine driver Esteban Ocon has revealed he vomited after 15 laps of the Qatar Grand Prix but refused to give up as he battled on to finish seventh at the end of the 57-lap race.
The event took place in temperatures of over 31 degrees Celsius (88 Fahrenheit) and high levels of humidity on Sunday night.
Williams driver Logan Sargeant was forced to retire his car 17 laps before the finish after feeling unwell in the cockpit.
Sargeant was cleared by the medical team at the circuit, but was diagnosed with intense dehydration and his team said he had already felt unwell earlier in the week.
Ocon, speaking to reporters after the race, revealed he was dealing with symptoms long before the halfway point of the grand prix.
"I was feeling ill by lap 15 or 16 -- I was throwing up for two laps inside the cockpit," he said. "And then I was like, s---, that's going to be a long race.
"I don't know, I tried to calm down, I tried to remember that the mental side in sport is the strongest part of your body, and I managed to get that under control and finish the race.
"But honestly, I was not expecting for the race to be that hard. I can normally do two race distances, even in Singapore. Physically, like muscle-wise and cardio-wise, I'm always fine.
"I don't know, it was just like 80 degrees Celsius inside the cockpit this race. I don't think we probably do the best job in terms of not keeping the heat in the back, but dissipating it inside the cockpit where the driver drives, and I think that was probably the reason today why we felt so bad.
"But yeah. Glad that we finished the race. A hard one, well deserved, the maximum we could have done. A happy ending."
Asked if he considered retiring his car after vomiting, Ocon, who scored six points by finishing seventh, said: "It's not an option, retiring. I was never going to do that.
"You need to kill me to retire. It's true."
Aston Martin driver Lance Stroll said he was struggling to maintain his vision and nearly passed out in some of Qatar's high-speed corners in the second half of the race. He finished ninth on the road but dropped to 11th in the final standings after penalties for exceeding track limits were applied.
"It's ridiculous," he said. "In these temperatures, everything goes blurry. In the last 25 to 30 laps everything was blurry in the high-speed corners with blood pressure dropping and just passing out, basically, in the car with high-speed corners and high g-forces."
He said the FIA's decision to tighten track limits at Turn 12 and 13 in an attempt to protect Pirelli's tyres from the circuit's kerbs had only worsened the issue and contributed to his penalties.
"The kerbs now are painted [on the track surface] because they were worried about punctures with these high loaded g-force corners, so they painted the kerbs to make the track even narrower, so you are relying on your visual reference to the outside of the track and what that is.
"But the last 20 to 25 laps you can't really see anything because you are just fading as you are going through those corners. It's really a shame that after such a hard-fought race we only got 11th, because we finished ninth and the car felt good today."