from the effects of an awkward tumble he took during The Oval Test. The opener's vision was left blurred due to the concussion forcing him out of the ongoing ODIs.
He has been advised rest for 10 days.
"The doctors said if you are still dizzy and puking, these are clear symptoms of concussion," Gambhir told 'ESPNcricinfo'.
"If I looked down, I felt like puking. If I tried to focus on one object, that made me feel dizzy. The vision remained blurry," he explained.
Before this, Gambhir had hurt his elbow which forced him to sit out of the third Test, a decision that drew flak from some quarters with some former players suggesting that he could have played through pain and helped India's cause. The team was whitewashed 0-4 in the Tests.
"Look, you are not just blocking, which is what was required at Lord's. This was a new Test. It was not just about time, you had to score runs, you had to field, you had to last five days," Gambhir explained.
"The pain in the elbow was massive. It might be easy for an outsider to say that it is not broken and he can play, but the pain was too much. I experienced it during the nets and the throwdowns before the match.
"And an elbow injury is different from a hand injury, which was the case in Cape Town. You can bat with a swollen hand, but it is very difficult to bat with a painful elbow," he added.
"You can't even get down to thinking of the performance when you have batted through injury three out of the six innings," he retorted.
Gambhir said playing with the concussion after that would have jeopardised the team's chances even more.
"If your vision is blurry, if you can't focus on one object, if you can't judge the pace of the ball or its trajectory, not only are you putting yourself at risk, you are also letting your team and your country down," Gambhir said.
"During the (Oval) Test I did what I had to do. There was no choice but to bat, but after that, even when taking throwdowns, I struggled with the vision."