A woman collapsed and died when staying as an inpatient at a private mental hospital after medical staff noted she had been drinking excessive amounts of water, an inquest has heard.

Lillian Lucas, 28, known as Lily to her family and friends, died in September 2022 after being found unresponsive in her room at Milton ward at the Cygnet hospital in Kewstoke, near Weston-super-Mare, where she had been an inpatient since June.

Lucas, who lived in Malmesbury, Wiltshire, was a mental health nurse who had previously been diagnosed with schizophrenia and had been admitted to various hospitals numerous times in the years before her death, the inquest heard.

The jury inquest into Lucas’s death at Avon coroner’s court was told that in early September 2022 while at the Cygnet hospital she was prescribed clozapine, an anti-psychotic drug which, due to her medical training, she was aware could have severe side-effects.

She and her father, Paul, raised concerns about the prescription of the drug, the jury was told.

On 8 September 2022 after drinking “excessive amounts of water”, she was found unresponsive in her room and transferred to Bristol Royal Infirmary (BRI), the jury heard. She died the following day.

A doctor who had previously treated Lucas spoke at the inquest about the possible reasons why someone would drink excessive amounts of water.

Dr James McIntyre, a consultant psychiatrist who had treated Lucas before her admission to the Cygnet, said psychogenic polydipsia – a mental disorder that can cause some people to have an uncontrollable urge to drink water – could be caused by the side-effects of anti-psychotic medication or as a symptom of the psychosis itself.

The coroner Dr Peter Harrowing read a statement from Lucas’s mother, Mary Curran, who was present in the court. Curran said in the statement that the ward at the Cygnet was understaffed and “relied on agency staff”.

“Generally, it seemed that the ward was understaffed, which meant that Lily was unable to access the care and support that she required for her needs,” the statement said.

“Lily would frequently comment that the ward was short-staffed. Milton ward relied heavily upon agency staff, which in turn affected Lily’s loneliness. Lily would frequently wait all day for a few minutes’ escorted leave in the grounds. On occasions, Lily would be refused escorted leave due to being short-staffed.”

Curran told the jury: “I was surprised by the lack of compassion on the ward,” which she argued “contributed to the deterioration of her mental health”.

On 5 September, as her condition deteriorated, Lucas was prescribed clozapine.

“Lily had always feared being prescribed clozapine,” Curran said in her statement. “Lily was aware of the possibility of severe side-effects.”

Her father, Paul, visited on 5 September and voiced concerns to the medical staff about the “severity of risk” of side-effects, the inquest heard.

He was told by a doctor that the benefits outweighed the risks and assurance was provided that his daughter would be monitored, the jury was told.

Curran said in her statement she received a number of calls from her daughter on 7 September complaining she was nauseous.

“I asked her if she had told the treating team she felt unwell and she said she had told them on three or four occasions, but they weren’t doing anything in response,” Curran said in her statement.

Lucas called again on 8 September with the same complaint. “This was the last time we spoke,” Curran said in her statement. Lucas sent a text message to her mother later that morning saying “one more sleep” as she was due to visit her on 9 September.

Later on 8 September, a female member of staff at the Cygnet called Curran to say her daughter had been drinking large volumes of water, and had collapsed on the floor, suffering a seizure and a heart attack. Resuscitation was attempted for 45 minutes and she was transferred to BRI.

“The consultant in the ICU told me excessive consumption of water was the probable cause of Lily’s death,” Curran said.

“The loss we feel as a family is unbearable and immeasurable,” the jury was told. “As a family we have often felt lost, alone and out of depth. We feel let down as a family and do not want that to happen to anyone else.”

Curran read a pen portrait of her daughter, who graduated from the University of the West of England in 2017 as a mental health nurse, to the jury.

“Lily was beautiful, loving, generous and hilarious,” she said. “She was so carefree and fun, and so full of mischief.”

“One of her nursing colleagues described her as a fierce and progressive mental health nurse. Lily knew what good nursing care and support looked like.”

The inquest continues.