Two junior doctors had responsibility for more than 400 hospital patients during a night shift.
Board papers from Derriford Hospital, Plymouth, reveal that an anonymous doctor raised concerns about the "very unsafe shift".
The report said the doctor was pulled from a breast surgery day job at 11:00, so they could cover nights.
Plymouth Hospitals NHS Trust said having two rather than three doctors on 2 May this year was an "exception".
In the papers presented to the board in July, the doctor wrote they were told to do the night shift "as there would otherwise only be a single SHO (Senior House Officer) looking after all of the medical patients in the hospital".
They continued: "After discussion with my consultant we reluctantly agreed that the best measure from a patient safety perspective would be for me to attend this shift, despite it being unsafe and bad for my personal training/development.
"Unfortunately, I did not manage much sleep before coming in for the night due to the short notice.
"Between myself and the other SHO on ward cover we were responsible for the care of 436 patients between the two of us, while carrying the crash bleep which covers the whole hospital."
Dr Peter Rowe, deputy medical director for Plymouth Hospitals NHS Trust, accepted it had difficulties recruiting junior doctors, with 68 current vacancies.
He said such incidents happened "rarely" and the doctors in question had responsibly for only a small number of "acutely unwell" patients, and not for any new admissions.
"Of course, two out of three is not good and that's why this was reported as an exception but it's not the generality, and it's not the whole hospital. It's important to realise that," he said.
"These two individuals were working hard, and they were working harder than usual because only two of three of them were present, but they were supported by the greater doctors and everyone was aware of this was the position on that particular night."