Manageress Lynette Taylor sent three of her staff at the store in Blaby, Leicestershire, to hospital when they began vomiting. She then called the fire brigade, who said the mystery fumes were possibly toxic and that the store should be closed until the cause was found.
The shop remained shut for two days as environmental health experts and electricians searched for a cause, with the chief suspect being a faulty chiller unit.
However, area manager Andy King said the cause still remained a mystery.
Lynette added: “Thankfully, no customers were affected, but it was very worrying to see the three staff members so ill.”
The staff were taken to Leicester Royal Infirmary, but were later allowed home.
The store has now re-opened and is trading normally, after health chiefs gave it the all-clear.