A Buckingham Palace spokeswoman declined to discuss in detail her condition, but said she remained in "good spirits". Professor John Cunningham, physician to the Queen, was pictured smiling broadly as he left the hospital a few hours before his patient was discharged.
The Palace spokeswoman confirmed that the Queen's diary for this week would remain suspended as she recovered from the illness. "Engagements cancelled or postponed this week remain so," she said. "Next week we'll have to see, as she has only just been released from hospital."
The Queen's illness forced her to cancel a trip to Rome to meet the country's president Giorgio Napolitano for a private lunch on Thursday. And a Buckingham Palace reception on Tuesday for MPs and MEPs will now be hosted by the Duke of Edinburgh and the Countess of Wessex.
The Queen has a number of events next week, including the annual Commonwealth Observance multi-faith service at Westminster Abbey in London. At the engagement, which takes place on Monday and is usually attended by other senior royals, the Queen's pre-recorded video message to the family of nations will be broadcast to the 2,000-strong congregation.
Soon after leaving hospital the Queen's royal standard was raised above Buckingham Palace, indicating she would be spending the night at her official London home.