LONDON (AP) — Queen Elizabeth II returned home yesterday after receiving treatment for a stomach infection that prompted a brief and rare hospitalisation for the 86-year-old monarch.

A smiling Elizabeth walked unassisted out of King Edward VII Hospital yesterday afternoon, bidding farewell to staff outside. She was then driven away in a motorcade.

"The queen has left the King Edward VII's Hospital having been admitted briefly as part of the assessment of symptoms of gastroenteritis," the palace said in a short statement issued after her release.

Gastroenteritis is an inflammation of the stomach, the intestine, or both, and it is generally caused either by food poisoning or the norovirus, a common winter vomiting bug that affects several hundred thousand Britons every year but which is very rarely dangerous.

The queen canceled engagements for this week due to the illness, although she could be back to work by next week. Doctors who weren't involved with Elizabeth's treatment believe she may have been hospitalised as a precaution.

It was the monarch's first hospitalisation in 10 years, but it set off few alarm bells in Britain, where she is seen as being in excellent health. Although not as physically active as she used to be, the queen still maintains a demanding schedule.

Unofficial court figures indicate she carried out roughly 400 official engagements in 2012 -- ranging from weekly one-on-one meetings with the prime minister to gatherings of 100 or more people.

Britain's royal-obsessed tabloids all wished Elizabeth well, while the Daily Mail's royal correspondent, Richard Kay, wondered whether the country expected too much from Elizabeth. Kay noted that the queen — and her 91-year-old husband, Prince Philip — spent hours on their feet in the cold and pouring rain during the river pageant meant to mark her Diamond Jubilee last year.

"Many may today be asking the same question posed after that extraordinary display of quiet physical and moral courage: Are we asking too much of the Queen?" he wrote.

But most Britons seemed to take Elizabeth's illness in stride. There were no concerned crowds of well-wishers gathered outside the hospital Monday morning — only news media keeping an eye out for royal visitors coming to pay their respects.

Meanwhile, the royal universe was returning to normal. Soon after the queen left the hospital, the royal standard — the four-part flag meant to indicate that the queen is in residence — was raised above Buckingham Palace in London.