A "dangerous fantasist" who posed as a nurse at the Blenheim Palace Horse Trials has been jailed for four years.
Cassandra Grant, 39, of Mulberry Walk, Bristol, was involved in injecting an injured rider at the Oxfordshire event on 13 September last year.
Oxford Crown Court heard how she repeatedly lied about having medical and mental health qualifications.
Judge Peter Ross said it made his "blood run cold" to think of Grant "getting her hands on a patient".
She pleaded guilty to fraud and common assault.
The court heard Grant had previous fraud convictions for impersonating a doctor in order to prescribe herself treatments.
She also started a Facebook group claiming she was terminally ill and needed donations towards hospice care, the court was told.
Michael Roques, prosecuting, said Grant put herself forward as an A&E nurse at an information day ahead of the Blenheim event, and her qualifications were never checked.
He said on the day of the trials she was involved in "a number of different medical situations", including a person having a heart attack.
On that occasion she caused concern among the genuine medical staff by shouting "cardiac arrest" loudly and had to be told to stop, Mr Roques said.
She also was present when morphine and anti-sickness medication were injected into an injured rider who had fallen off her horse, though someone else administered the drugs.
Anne-Marie Critchley, defending, said Grant had been diagnosed with factitious disorder - a condition in which a person falsely claims to have a physical or mental illness.
Judge Ross said although no one was harmed, Grant was a "dangerous fantasist" who had put members of the public at risk.
"A life-saving opportunity might well have been missed on the assumption by your colleagues that you were qualified to deal with it," he said.
The judge added that it was "a matter of some surprise that the most basic of checks, such as were you on the nursing register, were not made".
A spokesperson from Blenheim Horse Trials said as soon as organisers were made aware Grant was not a medical professional they told the police.
"As a result of this investigation, the checking procedures of qualifications for skilled personnel have been revised and strengthened," they added.
A one-year suspended sentence for Grant's previous offences was activated, which will run consecutively to her three-year sentence for fraud.