The Queen attended a number of engagements before spending a night in hospital on Wednesday.
She was ordered to rest by doctors and advised to miss a trip to Northern Ireland following her busy schedule.
Here is what the 95-year-old monarch has been up to since her return to Windsor Castle at the start of October:
– October 6: The Queen holds two virtual audiences at Windsor with the Greek ambassador and the ambassador for Belize.
She meets Canadian troops from 1st Regiment Royal Canadian Horse Artillery, and later has a telephone audience with Prime Minister Boris Johnson.
– October 7: The Queen, with the Earl of Wessex, launches the Queen’s Baton Relay for the Birmingham 2022 Commonwealth Games from the forecourt of Buckingham Palace.
– October 12: The Queen, accompanied by the Princess Royal, attends a Westminster Abbey service of thanksgiving to mark the centenary of the Royal British Legion.
She uses a walking stick at the abbey – the first time she has done so at a major event.
– October 13: The monarch has a face-to-face audience with pianist Dame Imogen Cooper to present her with the Queen’s Medal for Music. She also holds three other audiences.
– October 14: On an away day to Cardiff, the Queen delivers a speech at the sixth session of the Welsh Senedd.
– October 16: The Queen enjoys a day at the races at Ascot, and presents the trophy after the Queen Elizabeth II Stakes during the Qipco British Champions Day.
– October 18: She holds a virtual audience with the new Governor-General of New Zealand, Dame Cindy Kiro.
– October 19: The Queen has three engagements – two virtual audiences with the Japanese ambassador and the EU ambassador, and then hosts an evening reception at Windsor Castle to mark the Global Investment Summit.