The Queen did not attend church on Sunday after being advised by doctors to rest, the Sun has reported.
The monarch, 95, was expected at a Sunday service at All Saints Chapel in Windsor but was not in attendance.
She was said to be disappointed not to be able to travel to Northern Ireland on Wednesday, and reluctantly took the advice of her doctors to get more rest.
It is believed the Queen is now saving her energy for the COP26 eco-summit which she is expected to attend when it begins next week.
It’s the first time Her Majesty has missed prayers at the All Saints Chapel in Windsor since she returned from her summer break.
Watch: The Queen's Biography
Royal author Angela Levin told the Sun: “I am delighted she did not go to church because she is perhaps listening and agreeing to temporarily step back.
“Going to church on a Sunday sounds just a small event but it is a very big thing for the Queen and for any woman of her age,” she added. “She is very religious and it is very important personally for her to go to church every Sunday.”
Since the death of the Duke of Edinburgh in April, the Queen has had over 100 official engagements, with only Prince Charles and Princess Anne having a busier schedule in the last seven months.
The Sunday Times reported that the Queen is exhausted as she was maintaining a busy timetable of private commitments - as well as staying up late to watch TV.
The newspaper said the Queen has had “a constant flow of lunches and dinners with family and friends” this month because “she does not want to dine alone”.
After her hospital visit earlier this week, a Palace spokesperson 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.”
Watch: What will happen when the Queen dies?