The Queen is being treated in hospital for gastroenteritis, an infection of the stomach and large intestine.
The two most common causes of the illness in adults in England are the norovirus and food poisoning, according to the NHS. Common symptoms include vomiting, diarrhoea and dehydration.
It is not yet known if the Queen is suffering from viral or bacterial gastroenteritis but it is unlikely she is being given antibiotics as this prolongs the time it takes to settle the condition.
More top news
The ISIS execution gang fronted by 'Jihadi John' had two British extremists who learned radical Islam together in London, ITV News reveals.
Today started quite promising for many, largely dry and sunny.
Turkish deputy premier says 15,000 refugees from Syria have been admitted with a further 30,000 refugees being cared for across the border