This lead to severely low sodium levels, causing swelling in the brain, fatally injuring it.
Her medical cause of death was hyponatraemic encephalopathy, acute hyponatremia and psychogenic polydipsia.
Nottinghamshire Healthcare NHS Foundation Trust admitted eight failings in the care Michelle received while at Millbrook for the second time.
She was earlier admitted in 2018 following an acute mental breakdown.
The failings ranged from staff not adhering to trust policy when Michelle was tranquilised to inadequate observations as a result of being “distracted” by mobile phones.
The investigation into Michelle’s death also found a 10-minute delay in letting paramedics enter the building.
Following the inquest, coroner Laurinda Bower sent a prevention of future deaths report to trust CEO saying more people could die “unless action is taken”.
Ifti Majid, chief executive of the trust, offered his condolences and apologies to Michelle’s family.
He told the BBC: “We are considering the findings of the jury and the coroner.
“We acknowledge that there were aspects of care which were not of the quality they should have been and will address the concerns raised so that the experience for patients now and in future is improved.”
Psychogenic polydipsia
Psychogenic polydipsia is characterised by excessive water intake and is often seen in patients with psychiatric disorders and/or neurodevelopmental disorders.
The condition can kill as it swells your brain which can injure it.
This happens because water in the body causes the body’s salt levels to go down and the cells to swell and grow in size.
Swollen cells in the brain press against the skull and may lead to serious medical problems.