Queen Elizabeth left a London hospital today after a stomach infection forced her to check in Sunday and cancel or postpone a week's worth of engagements.
The queen, 86, experienced symptoms of gastroenteritis and received treatment at London's Kind Edward VII Hospital, according to Buckingham Palace. The palace says she was in "good spirits" before her exit and all signs suggested that her illness is not serious.
The queen first fell ill Friday but kept up her scheduled events through Sunday morning, after which she was driven to the hospital in a car, rather than an ambulance.
"This is a precautionary measure," a statement from the palace read this weekend. "She was not taken into hospital immediately after feeling the symptoms. This is simply to enable doctors to better assess her."
Gastroenteritis is an infection of the intestine and causes diarrhea and vomiting, according to doctors. It is usually treated with fluids, and symptoms often pass after two to three days, although the queen's age forced doctors to proceed cautiously.
"Age is a factor which makes us worry a bit more about when people have gastroenteritis, because it's more difficult for the body to maintain fluid balance. Once you get a bit older, your kidneys tend not to work as sufficiently," Dr. Anton Emmanuel, a gastroenterologist who works at Edward VII Hospital but is not treating the queen, told ABC News.
Emmanuel said doctors will monitor the queen's hydration levels and would let the infection pass through her system, but would aggressively treat any side effects she suffered, including fevers and cramps.
"There will be intravenous drip saline to replace the fluids the body is losing, very careful monitoring of the hydration status which we can do by clinical testing on the blood tests, and then treating symptoms and then waiting for the infection to break, which it usually does in two, three days," he said.
The queen held nearly a dozen engagements last week, and she takes pains not to have her schedule interrupted. She has cancelled only a handful of engagements over the years and has only visited the hospital about half a dozen times, according to local media.
She has cancelled or postponed a trip to Rome this week to meet the outgoing president of Italy, as well as a visit to a Royal Navy ship in London known as "The Queen's Frigate" Tuesday, and a military celebration in Wales Saturday. It is unclear whether these engagements will be back on.
The last time the queen visited the hospital was December 2003, when doctors operated on her knee to remove torn cartilage.
Outside the hospital door is one of the more unusual teams in the Metropolitan Police. Anthony Wallyn is Britain's tallest policeman at 7-foot-2. Standing beside him is the shortest officer in the Westminster Borough Support Unit: Tony Thich, who measures 5-feet-6. They are known as Big Tone and Little Tone.
The queen's husband, Prince Phillip, will maintain his schedule, attending an event by himself today, another sign that the queen's illness is not serious. Prince William, the Duchess of Cambridge and Prince Harry were travelling back from Switzerland after attending a friend's wedding.