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Brandy says a medical incident drove her offstage in Chicago Saturday night ... revealing a sudden wave of dehydration threatened to make her faint.
The singer-songwriter explained her sudden departure from her United Center show in an Instagram post Sunday morning ... telling her fans that -- after weeks of nonstop rehearsals -- she experienced feelings of dehydration during the show.
Brandy says she did return to the stage after initially leaving it ... but adds she couldn't connect to the tunes sonically -- and acknowledges it wasn't her best show by any stretch of imagination.
After leaving the show, Brandy says she went to a local doctor ... and she's taking proper precautions to avoid a situation like this in the future. Play video content
Brandy adds she's deeply grate