Sir Timothy Laurence, the Princess’s husband, and Zara Tindall and Peter Phillips, her children, were all on the estate at the time. Other members of the Royal family – the King, Queen, Prince Edward, Prince Andrew and Prince William – were notified last night.
The Princess is expected to be released from hospital later this week.
A spokesman said: “Her Royal Highness is recovering well, is in a comfortable condition and is being kept in hospital as a precautionary measure for further observation.”
Sir Tim went with her to hospital. Her engagements for the rest of the week will be cancelled, as will her participation in the State Visit and her upcoming trip to Canada at the end of this week.
A spokesman said: “On doctors’ advice, Her Royal Highness’s engagements for the week ahead will be postponed. Her Royal Highness sends her apologies to any who may be inconvenienced or disappointed as a result.”