Jason Roy said low sugar levels caused his dizzy spell in England's ODI victory over Pakistan at Southampton on Wednesday.
The Surrey star hit a solid 65 as England drew first blood in the five-match series, recovering his poise after seeking medical attention when feeling light-headed.
The 26-year-old was relieved to have avoided any serious problem, saying: "It was a case of not having enough sugar on me apparently, that's it plain and simple.
"I had a headache, felt a bit dizzy, they got the physio and the doctor on, they told me to get some sugar on board. I'll just remember in future on a hot day to be mindful of that.
"I was able to get my bearings, settle and reset myself and just go again."
England eventually won by 44 runs on the Duckworth-Lewis-Stern method after two late rain delays interrupted England's reply to Pakistan's target of 260-6.
When the rain forced an early abandonment, England were well ahead at 194-3, after Joe Root's 61 and an unbeaten 33 for Eoin Morgan.
They now move on to Lord's for the second match on Saturday, live on Sky Sports 2, but not before a briefing on the security situation in Bangladesh.
Captains Alastair Cook and Morgan and team members will meet with the ECB's security director Reg Dickason to review current security issues in the country, with a final decision expected this week.
The so-called Islamic State claimed responsibility for an attack in Dhaka last month which saw 20 hostages killed, including nine Italians.
Australia have cancelled senior and U19 tours to Bangladesh in the last year and Dickason has spent two weeks assessing the safety of players, supporters and media.