Sore Hamilton nearly missed Valencia race
The revelation came after the McLaren driver finished second to title rival Felipe Massa on the new urban city circuit.
"I've had a pretty miserable weekend, really," the 23-year-old told reporters.
Hamilton said he not only has the 'flu and fevers, he also woke early on Saturday morning with neck spasms, probably triggered simply by sleeping in an awkward position.
"It kind of nearly led to me not racing this weekend," he said, confirming that test driver Pedro de la Rosa had been put on standby to drive his number 22 car.
Hamilton said the support of his physiotherapist helped him struggle through qualifying and then Sunday's race, played out over 57 laps in hot conditions.
"It was so bad that I was struggling to basically stand up and so I had to have injections in my neck and take plenty of painkillers," he explained.
Although confirming his neck was sore as he spoke, Hamilton thinks he will be fit for the forthcoming Spa Francorchamps-Monza double header, which kicks off with the Belgian grand prix in two weeks.