Editor's note: Mark Saunders is a longtime reporter on the royal family, beginning his career at his hometown newspaper, The Windsor Express, where he became royal correspondent and covered more than 200 official royal engagements. He is the author of several books on the royals.
London (CNN) -- In public Buckingham Palace are putting on a brave face, insisting the queen's illness is little more than a stomach bug and her hospitalization merely a "precautionary measure."
But behind the castle walls there is cause for concern.
The main worry is dehydration, quite common for anyone suffering from gastroenteritis; usually it is treated by replacing lost bodily fluids with water.
But the queen is finding it difficult to keep any fluids down.
For this reason she was taken to the Edward 7th hospital in London, the first time she has been in hospital for 10 years, where she is currently hooked up to an IV drip.
Buckingham Palace have canceled all the queen's official engagements for the next week, including a high profile visit to Rome.
Senior advisers have spoken of their concerns to the Prince of Wales and it is believed the queen, who is 87 next month, will be asked to take things easier over the coming months.
Though the queen is always described as being in "robust" health, her advisers are acutely aware there will come a point when she has to slow down.
For this reason the Duke and Duchess of Cornwall have been taking on far more high profile engagements recently as they prepare for the day they will formally replace the queen.
A source inside Windsor Castle said: "Charles and Camilla have subtlety created a more regal air over the past year and are beginning to look, and act, like a King and Queen in waiting. Behind them the ever-popular William and Catherine have now progressed to being senior members of the royal family.
"If the queen is convinced to cut back on the amount of engagements she carried out she will do so with the knowledge the family 'firm' is well taken care of behind her."
The opinions expressed in this commentary are solely those of Mark Saunders.