Hamilton suffered with neck spasms and flu symptons but still raced to second place
Lewis Hamilton said problems with his neck had almost forced him to pull out of the European Grand Prix.
The McLaren driver, also suffering from flu-like symptoms, was second to Felipe Massa's Ferrari after having injections in his neck to alleviate the problem.
"Luckily I have a great doctor and a great team or I might not have made it," said the Englishman.
"As it was, it was pretty tough in the race and I had a lot of pain, but I don't think I lost time because of it."
Hamilton actually extended his championship lead despite not winning the race, but Massa leapfrogged team-mate Kimi Raikkonen as his closest pursuer.
Hamilton is six points clear of Massa, with Raikkonen 13 adrift of the lead after retiring with engine failure from fifth place after a disappointing race.
Hamilton said he believed his neck problems had been caused by the position in which he had slept.
He said it had been "touch and go" whether he raced, and that McLaren test driver Pedro de la Rosa had been on standby.
"I think the spasms started when I woke up at around 5am yesterday (Saturday) and they were so bad I was struggling to stand up," he said.
"I had to have injections in my neck and I took some painkillers and I got through it, but it was tough. Pedro was looking forward to racing, I know that."
Hamilton said he had been feeling unwell ever since arriving in Valencia on Thursday.
"I have had a miserable weekend really from the day I arrived - I have a lot of flu symptoms, a fever every day," he said.
"I have had low energy, just felt poorly with problems with the spasms in my neck which led to me being in doubt for the weekend and obviously for this race."
I still think I can come back this season
Hamilton said his neck was still sore but that he doubted it would be a problem for the Belgian Grand Prix in two weeks' time, despite the long, fast, demanding corners on the Spa-Francorchamps circuit.
Raikkonen's last victory came at the Spanish Grand Prix in April and after another dismal race in Valencia he conceded getting his title defence back on track will be difficult.
"There are still many races to go and it can change so quickly, but there is no doubt it won't be easy," said the Finn.
"Losing the points we could have got is not very good. We are in a bit of a worse situation in the championship.
"I am not too worried. I still think I can come back this season."