The world's oldest and longest-reigning monarch, 95, stayed in hospital overnight on Wednesday but returned to Windsor Castle, to the west of London, the following day. Officials said she was in good spirits and back at work.
The queen routinely attends the All Saints Chapel in the grounds of Windsor Great Park. The Sun said the queen wanted to rest so she would be able to attend the U.N. climate conference in Scotland.
Buckingham Palace declined to comment.