Nearly a quarter of all accidents to patients receiving NHS care in England occur at night, a survey has concluded.
Nearly a quarter of lapses happen at night
Analysis of National Patient Safety Agency data found 140,000 incidents in 2006/7 between 10pm and 6am, when there are no scheduled tests or treatments.
Falls, trips and slips were the most common source of problems, according to the Reader's Digest survey.
Patient groups linked the problem to staffing, but the NHS safety watchdog denied there was more risk at night.
Joyce Robins, of Patient Concern, said: "All too often patients, particularly the elderly, are not given the help they need at night.
"This is a time when people should be safely asleep. But when they need help with things such as going to the toilet there is no-one there.
"They then have to try to go themselves but end up falling. And these falls can be quite serious."
Reader's Digest looked at figures from the National Patient Safety Agency from April 2006 to March 2007.
They showed that 22% of just under 700,000 so-called patient incidents, such as medication errors, surgery mistakes and falls, happened at night.
During this time there are no scheduled operations, consultations or tests, the report said.
Accidents such as slips, trips and falls were the most frequently reported night-time incident, accounting for 60% of the total.
Problems with admission, transfer or discharge represented 6% of night-time incidents, while treatment errors accounted for another 6%.
A further 6% of all incidents during the night were to do with medication errors.
NPSA medical director Dr Kevin Cleary said there was no evidence that patients were at a greater risk of incidents at night than during the day.
He said the prevalence of trip and fall-related incidents was being addressed by national campaigns and guidance on good practice.
But he added: "The NHS provides 24-hour care and therefore some incidents will occur at night."