Beloved British Queen Elizabeth II was hospitalized Sunday, after two days of suffering from the symptoms of a nasty stomach infection known as gastroenteritis.

The diagnosis, first reported by Buckingham Palace on Friday, has led the 86-year-old monarch to cancel a two-day trip to Rome scheduled to start Monday, as well as a number of appearances, while she recuperates.

Gastroenteritis is frequently mistaken for the "stomach flu," according to the U.S. National Institute of Diabetes and Digestive and Kidney Diseases. It is identified by a range of symptoms -- including abdominal pain, chills, diarrhea, fever, headache, and vomiting -- that are most often associated with influenza and other more well-known stomach bugs.

"Gastroenteritis is an inflammation of the lining of the intestines caused by a virus, bacteria, or parasites. Viral gastroenteritis is the second most common illness in the U.S.," the institute wrote. "The cause is often a norovirus infection. It spreads through contaminated food or water, and contact with an infected person. The best prevention is frequent hand washing."

The institute went on to explain that "most people recover with no treatment," although the effects can be more dramatic in elderly people.

The top-flight medical staff tending to Queen Elizabeth II's health this week at King Edward VII Hospital in London will likely focus on making sure she ingests enough fluids, as dehydration is one of the biggest problems associated with gastroenteritis.

Most people are able to quickly recover from gastroenteritis by ensuring that they get enough fluids and slowly return to a normal diet, according to WebMD.

"But for others, such as babies and the elderly, loss of bodily fluid with gastroenteritis can cause dehydration, which is a life-threatening illness unless the condition is treated and fluids restored," WebMD explained.

As a result, it is very important that doctors keep an eye on Queen Elizabeth II's hydration level to make sure she doesn't lose too much fluid.

The U.K.'s National Health Service has said the most common causes of adult gastroenteritis are food poisoning and norovirus, which is a common stomach bug that between 600,000 and 1 million British citizens host each year, mostly during winter months when people spend much of their time indoors, the Associated Press reported.

Dr. Christopher Hawkey of the University of Nottingham's faculty of medicine and health sciences told AP that if the queen's physicians decide she is not retaining enough fluid, she will likely need to undergo intravenous rehydration, assuming she isn't already doing so.

"Not everyone can keep up with oral hydration, so it is pretty routine to go to hospital and have a drip and wait for the thing to pass and keep yourself hydrated," Hawkey said. "It's very infectious and strikes in winter because people are indoors and it spreads more easily."

While the effects of viral gastroenteritis usually pass after a couple of days, the impacts of bacterial gastroenteritis -- caused by bacteria such as E. coli and salmonella -- can last for more than a week, posing a greater threat to a patient's health, according to WebMD. It is not yet publicly known what caused the queen's current bout with gastroenteritis.

The announcement that Elizabeth II is in hospital has come as a surprise to many Britons, as the queen is known for her long history of of avoiding health issues. The monarch has ruled since 1952, and she hasn't been hospitalized since 2003, according to a representative who spoke to AP. However, the rep noted, the queen did cancel an event about five months ago because of an issue with her back.