The woman was left in a locked room with no mattress or pillow during an incident the SDHB said was "highly challenging" but for which it says it is sincerely sorry.
Since the 2013 event it had provided "extensive additional and ongoing training" for staff.
Details of the event have come out in a report from the office of the Health and Disability Commissioner.
The report says the woman, who was in her late teens at the time, was taken to Wakari by police after she left a clinic she was to stay at under a compulsory in-patient treatment order.
She left after a disagreement with another patient, refused to return and was finally located in a tree by police, having self-harmed.
She was taken to Wakari, where she struggled and, it was recorded at the time, tried to bite staff.
There was no bed available in the locked unit at the hospital, so she was transferred to a secure unit under police restraint, as she continued to struggle.
When she arrived at the secure unit at 8.30pm she was placed in seclusion and her clothing was removed.
She was not given a tear-resistant gown to wear or provided with a mattress or pillow, and was left with only a tear-resistant blanket and a cardboard bedpan.
She was checked every 10 minutes and lights were left on overnight.
She was eventually given a gown at 11am the next day, and three hours later was released from seclusion and returned to the clinic.
The woman complained to the Health and Disability Commissioner in 2017 about her treatment while in seclusion.
In the report, released this week, Mental Health Commissioner Kevin Allan found staff failed to comply with seclusion guidelines and to provide nursing care of an acceptable standard.
"I am not able to make a finding that the denial of clothing and bedding was a punitive action or intended to humiliate [her]; however, I consider that these actions were unacceptable and unkind."
The manner of seclusion meant the SDHB failed to respect her dignity and independence, he said.
The woman told the commissioner she accepted she presented a significant risk to herself, but did not believe that risk necessitated being placed in seclusion or the treatment she received while there.
"It was probably the worst, most humiliating and dehumanising thing I have ever experienced and it makes me immensely terrified of getting unwell again.
"I believe I could have been managed on a locked ward without being secluded.
"What I experienced on that occasion was incredibly dehumanising and continues to affect me."
Expert adviser to the commissioner Anthony O'Brien concluded it was hard to see any clear reason for removing all her clothes and not providing her with a gown, mattress or pillow, especially for such a long period.
"Apart from having to endure the discomfort of sleeping on the floor, with no support for her head, it is undignified for anyone to be deprived of all clothing.
The SDHB was ordered to train its mental health staff in appropriate restraint and session practices, and review its seclusion guidelines and policies, particularly around things people should be provided with when placed in seclusion, such as clothing and bedding.
It was required to write a written apology to the woman.
Mental health, addictions and intellectual disability nursing director Heather Casey said yesterday the event was "highly challenging, and we acknowledge the ongoing distress it has caused to the person involved".
Clinical staff work hard to ensure people were cared for and kept safe, but during the event processes were not followed, she said.
