According to sources, the singer was rushed to Priory clinic suffering from exhaustion.
'I was having a cigarette break when a whole load of ambulances arrived.
'Everyone was saying, 'Who's that''? Then I saw her and it was Susan Boyle. I was gobsmacked,' the Sun quoted a source as saying.
A spokeswoman for the show said: 'Following Saturday's show, Susan is exhausted and emotionally drained.
'She has been seen by her private GP, who supports her decision to take a few days out for rest and recovery. We offer her our ongoing support and wish her a speedy recovery,' she added.
A show source said: 'It's very tough, Susan is emotionally drained -- she gave it her all and is absolutely shattered.
'Simon Cowell spoke to her backstage on Saturday night and told her she had everything going for her -- a record deal, an American tour. But it's up to her, she has to see what she wants.
'We do realise that we have a care of duty to look after her,' the source added.
Text: ANI | Photograph: David Moir/Reuters