The palace said, in a statement, that the 96-year-old queen was “resting at Balmoral Castle”.
While a source in the royal palace said that the queen’s family was informed of her health condition.
The Queen met the new British Prime Minister, Liz Terrace, on Tuesday.
“The entire country is deeply concerned by the news from Buckingham Palace,” she wrote on her Twitter account, Thursday.
She added, “My thoughts and those of people across the UK are with Her Majesty and her family at this time.”