The Queen's sickness was first announced on Friday, and she spent yesterday resting at Windsor.
Her Majesty had been due to attend a Welsh military celebration in Swansea during the country's St David's Day celebrations on Saturday, but was forced to cancel the plans.
The Queen, who is 86, has undertaken a number of engagements during the last week.
On Tuesday she met the Archbishop of Canterbury at Buckingham Palace, and on Thursday she presented a host of Olympic stars with honours during an investiture ceremony.
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