Queen Elizabeth II spent Wednesday night in hospital for preliminary medical checkups and has now returned to Windsor Castle.
The 95-year-old queen returned from a private hospital in central London for lunch on Thursday and is "in a good mood", the palace announced.
The Queen had canceled a visit to Northern Ireland on Wednesday, rtv21.tv reports.
She was given medical advice to rest a few days after a busy schedule of public engagements.
It is the first time the queen has been in hospital since 2013, when she suffered symptoms of gastroenteritis.21Media