Jason Ketley was subjected to a vicious rat attack as he lay sedated in hospital, his parents have claimed.
Vulnerable patient Ketley, who has a mental age of two, was bitten dozens of times all over his back and neck.
Heavily sedated, the attack only ended after nurses spotted the rodent hanging from the 42-year-old's neck, as he wandered down the hospital corridors the Daily Mirror reports.
The animal was immediately killed, and Ketley taken to Epsom General Hospital for diphtheria, tetanus and polio injections.
Ketley's mother, Pat Boardman, has dismissed hospital claims that the animal was a field mouse and not a rat, describing her son's injuries as "large open bite marks" to the Mirror.
She expressed disgust at the incident, telling the newspaper that her son was "helpless and terrified". According to his mother, Jason was so traumatised by the experience that nurses had to show him the carcass of the dead animal, to reassure him that the rat could no longer hurt him.
Ketley, who also suffers from bipolar disorder, was on ward at a specialist care unit in St Ebba's hospital in Surrey. The incident occurred in November, and his patients have made a complaint to Surrey and Borders Partnership NHS Foundation Trust.
Jo Young, Director Quality and Nursing at Surrey and Borders Partnership NHS Foundation Trust, said:
“The events described here are genuinely shocking and I would like to reassure Mrs Boardman that we are taking her concerns extremely seriously. This is why we have logged the events as a serious incident and are conducting a detailed investigation.
“Our records indicate that a mouse was seen in the house in November and that pest control was alerted immediately but we are unable to provide a complete response to all the concerns raised until we know the outcome of our investigation.
It is not the first time that rat attacks in hospitals have been recorded, although fortunately in Britain they are extremely rare.
In January, a paralysed man in India was subjected to a vicious rat attack as he lay helpless in a bed in Jodhpur. The rodent reportedly gnawed on the 70-year-old's ears, lips and nose, his family finding the injured man in his bed the following morning.