By Karl Mercer Health Correspondent, BBC London
Patients and staff at two of London's biggest hospitals have described a week of chaotic scenes caused by a computer meltdown during the recent heatwave.
Operations at Guy's and St Thomas' Hospital Trust were cancelled after IT servers broke down in 40C (104F) temperatures on 19 July.
One cancer patient told BBC London she was almost given the wrong drugs.
Guy's and St Thomas' NHS Trust has apologised and pledged to hold a full investigation.
The heatwave wiped out the hospitals' two main computer systems within an hour of each other.
While they have since been restored, problems have remained and may continue into next week.
Jennifer, who did not want to give her surname, was in St Thomas' Hospital receiving treatment for cancer. She said she was told on several occasions that the computers were not working and that the place "was in chaos".
She said: "I've never been so weak, dependant and vulnerable in my whole life.
"I couldn't walk or get out of the bed in the days after the surgery, so lying there aware that there was a systems failure - even though the doctors and nurses were on the whole being amazing - I was very anxious.
"I overheard a group of pharmacists talking about how worried they were."
She added: "On two occasions I was confused for being another patient. Once in the middle of the night a nurse woke me up to try and give me medication I had never heard of.
"After quite a long argument with this nurse it transpired she was standing with a different patient's paper record.
"Another occasion a surgeon burst into my room to tell me he had been in my operation and that my appendix had ruptured.
"Again after another slightly long argument it transpired he had got the wrong person and was very apologetic."
Numerous operations and procedures have been cancelled as a result of the IT problems.
Earlier this week an anonymous doctor told BBC London staff were not able to read any historical notes from patients.
Names were also being misspelt meaning that scans did not show up.
Reacting to Jennifer's experience, Guy's and St Thomas' chief nurse, Avey Bhatia, said she hoped the internal investigation would restore the confidence of patients.
She said: "I want to apologise to Jennifer. That is not the experience we expect patients to have here at Guy's and St Thomas'.
"We are terribly sorry that these incidents occurred. Maintaining patients' safety is an absolute priority."
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