The Queen spent Wednesday night in hospital for preliminary medical checks and is now back at Windsor Castle "in good spirits", Buckingham Palace said.
The 95-year-old monarch returned from hospital at lunchtime on Thursday, the palace said.
The Queen was said to be "disappointed" after cancelling a visit to Northern Ireland on Wednesday.
She was given medical advice to rest for a few days, after a busy schedule of public engagements.
In a statement on Thursday night, Buckingham Palace said: "Following medical advice to rest for a few days, the Queen attended hospital on Wednesday afternoon for some preliminary investigations, returning to Windsor Castle at lunchtime today, and remains in good spirits."
https://www.bbc.co.uk/news/uk-59004426
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not sounding good