Boyle was admitted to London's Priory Clinic a day after she finished behind a male dance group on the show Britain's Got Talent, the Sun newspaper reported.
"Nobody has had to put up with the kind of attention Susan has had. Nobody could have predicted it," one of the show's judges, Piers Morgan, told breakfast TV show GMTV. "It has been crazy, she has gone from anonymity to being the most downloaded woman in history."
Boyle was favored to win the show's final - watched by more than 19 million people - after a clip from her first appearance became the fifth most-watched in YouTube history, viewed more than 220 million times.
The discovery that a woman from a small Scottish town was capable of singing very well on a national stage turned Boyle into a modern-day Cinderella. On Oprah Winfrey's US television show, the singer had said she was "loving every second" of her unexpected stardom.
But much of the media storm surrounding her debut was laced with snide commentary about her looks, her social awkwardness and her remark that she had never been kissed.
Scotland's First Minister Alex Salmond was scathing about the media pressure, saying there were "elements of a press who like nothing better than to build people up and then drag them down."
Television company TalkbackThames said Boyle was "exhausted and emotionally drained" and was taking a few days off.
"She has been seen by her private GP, who supports her decision to take a few days out for rest and recovery," the company said.
London police would not confirm the report that Boyle was admitted to a clinic, but said doctors were called to assist a woman under the Mental Health Act, and the woman went voluntarily to a clinic.
The Priory - one of a chain of clinics known for treating celebrities including fashion model Kate Moss and musician Pete Doherty - offers treatment for a range of psychiatric problems as well as drug and alcohol addiction.
Boyle had looked tense and uncomfortable after giving a strong final performance Saturday night with "I Dreamed a Dream" from Les Miserables - the same song she chose for her April debut.
When Diversity was announced as the winner, she looked relieved and relaxed. Smiling broadly, she said the best act had won and wished the dance group all the best.
Boyle drew 20.2% of the 4 million votes cast in the final, behind Diversity's 24.9%.
