A hospital trust gave no assurance that errors that led to a patient with dementia being left on a trolley in A&E for more than 33 hours followed by an assessment unit for 42 hours would not happen again, according to a report.
The incident is one of many detailed by the Parliamentary and Health Service Ombudsman, which has published summaries of the 618 complaints it completed investigating in October and November last year - most of them about the NHS.
Other investigations looked at how East of England Ambulance Service paramedics left a frail woman in her 80s home alone without adequate support although she was suffering with sickness and diarrhoea and had soiled herself, and into how a man with dementia died soon after being unsafely discharged from A&E on Christmas Day.
Around 80% of the ombudsman's investigations are about the NHS in England, while the rest are about UK Government departments and their agencies. During this two-month period it upheld two out of five (41%) of the complaints it received.
Most of its NHS investigations were about hospital trusts, followed by GP practices and then mental health trusts.
The investigation into the dementia patient found University Hospital of North Staffordshire NHS Trust's response to the complaint gave no reassurance that the failings would not happen again.
Following the ombudsman service's investigation, the trust acknowledged and apologised for its failings and agreed to explain what action it has taken or proposes to take to ensure that there is learning from what happened.
Another family complained after they were left for five hours behind a curtain separating them from where their mother was being treated, hearing her have several cardiac arrests as well as being mocked by nursing staff at University Hospitals Birmingham NHS Foundation Trust.
After her death they were told they could see her, but had to wait another 45 minutes behind the curtain until they decided to take matters into their own hands and go into the cubicle.
The ombudsman service's investigation found that there were failings in how staff communicated with the patient's children and how they treated them and that the trust's complaint handling fell short of the expected standards.
Parliamentary and Health Service Ombudsman Julie Mellor said: "These cases show the impact that service failure can have on individuals and their loved ones.
"These case studies - which are a snapshot of our work - show the wide range of unresolved complaints we look at, many of which should be resolved by the organisations locally, without people having to refer the complaint to us.
"Good complaint handling has to start from the top, and leaders will recognise the valuable opportunities complaints provide to really improve the service they are delivering.
"Many people complain about public services to enable lessons to be learnt because they don't want the same thing to happen to somebody else."
Other complaints summarised in the report included those about the UK Border Force, UK Visas & Immigration, the DVLA, and the Highways Agency.
The ombudsman service investigates approximately 4,000 complaints a year, upholding around 37%.