The nurse found he was breathing at a normal rate and appeared to be asleep. She put a blanket over him and, with a second nurse, assessed his breathing, colour, response, position and comfort.
They left him on the floor as it was not unusual for patients to sleep on the floor.
"They did not consider the possibility that the man might have fallen," said the commissioner's office.
After the hand over to the morning shift a third nurse checked him, again concluding he appeared to be asleep, was breathing regularly, was of satisfactory colour, and that there was no cause for concern.
Around 1pm, three nurses lifted him into a chair.
The head afternoon nurse was told the man was still asleep due to over-sedation. Nursing observations were repeated and he was put into bed. He did not respond to staff and a doctor who checked him arranged an ambulance transfer to a public hospital.
He had a CT scan and a large subdural bleed was identified on his brain. It was considered too large to treat and he died that evening.
The overnight and morning-shift nurses who assessed the man failed to do so adequately, Ms Baker said.
She criticised staff for not telling the man's family of his admission to the psychiatric hospital and held that he should not have been prevented from leaving.
She also criticised the DHB's environment, culture, and failure to ensure staff were familiar with policies and asked it to audit changes it had implemented since the man's death. Ms Baker recommended a number of nurses undertake further training.