AN 80-year-old man was left waiting more than 16 hours for emergency treatment on New Year's Day after falling in the bathroom.
People are waiting too long in A&E departments because there are no beds for them on wards, and because many of those hospital beds are taken up by patients who are waiting for their social care arrangements.
NHS bosses apologised to the family, citing "significant pressures this winter because of a high number of complex cases and respiratory illness".
NHS Scotland figures and the health secretary, Shona Robison, pointed to an increase in flu as part of the reason for the poor results.
The health minister said that the current pressures on the service were not "just about flu", but she added that "clearly it will be a key factor over the coming weeks".
NNUH Chief Operating Officer Richard Parker said: "Recently published figures on our A&E performance against the four-hour target are unfortunately incomplete".
She added: "We have record staffing in Scotland's NHS and we're aiming to go further".
Health service data shows flu rates are continuing to rise, with one in five hospital cases suffering from the most deadly strain, dubbled "Aussie flu" after it fuelled the country's worst flu season for more than two decades.
In 2016/17, there were 21,340 beds in Scotland's hospitals, Ruth Davidson said - compared to more than 23,000 in 2012/13.
Meanwhile, Scottish Lib Dem leader Willie Rennie accused Ms Sturgeon of having a "brass neck".
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Ms Sturgeon responded: "What I say to Mr Wilson is very simple, I say sorry to Mr Wilson if that was his experience of the health service".
He added: "We are all proud of our NHS staff in enduring the conditions that have been created by Nicola Sturgeon, but is she really proud of what she has done to our NHS?"
NHS Forth Valley was the poorest performing health board with just 57.3% of patients dealt with within four hours.
Mrs May said flu was putting extra pressure on services and encouraged people to act on the advice the NHS is giving.
The higher flu rate in Scotland means the health service here is under greater pressure than the rest of the United Kingdom, she added.
He said Mr Wilson later spent 13 hours on a trolley in the accident and emergency unit.
"This year, with the current degree of winter pressure that we are feeling, this is the worst condition that I have ever seen the NHS in", Dr Adrian Harrop, an A&E doctor at Scarborough Hospital, said.
We are writing to you as Consultants in Emergency Medicine, Fellows of the Royal College of Emergency Medicine and as Clinical Leads (Consultants in charge) of our Emergency Departments, representing 68 Acute Hospitals across England and Wales.
"That's why we welcome Prof Sir Harry Burns' recent report on targets and indicators, and the principles he outlines, which we will now use to underpin further work to develop better ways of understanding people's wider experience of care".
"Our primary concern during this period was the safety of patients and the compassion and commitment of staff ensured that the level of patient care remained high through these challenging times".