The death of a woman who took her own life during treatment for schizophrenia and epilepsy was "avoidable", the health ombudsman has said.
Erica Henderson, from Cheltenham, died in 2016 aged 49 after failings by Gloucestershire Health and Care and Gloucestershire Hospitals NHS trusts.
Her sister Peggy Saleeb-Mousa said she had been "pushed from pillar to post".
Both trusts said they "fully accepted" the findings of the Parliamentary and Health Service Ombudsman.
Ms Henderson had been an inpatient at Wotton Lawn psychiatric hospital, in Gloucester, from November 2015.
Health ombudsman Rob Behrens said Ms Henderson's death was "avoidable" if the failings by the two trusts "had not occurred, it is less likely" Ms Henderson would have taken her own life.
Mr Behrens said: "There was a mix-up when she changed hospitals. She had a seizure. She didn't see a neurologist.
"She was sent back to the mental health hospital and she subsequently had an opportunity to take her own life, which she should not have had if the observations had been properly implemented."
The report said Ms Henderson should have been observed on a continual basis, her medication would have been reviewed, and the deterioration of her condition should have been noted and acted on with "sufficient urgency".
It continued: "We found that on the balance of probabilities, her final attempt to take her own life would not have occurred, and it is more likely than not that her death would have been avoided."
Ms Saleeb-Moussa said the trusts had failed to act on the increasing frequency of her twin sister's epileptic seizures and previous attempts to take her own life.
She said: "She killed herself because she couldn't control her seizures - because nobody could control them, or didn't want to.
"Medication got changed frequently. She went from one hospital to another hospital. She eventually got pushed between two different trusts.
"You can't imagine what it's like to sit and watch your twin sister - someone who looks like you, behaves like you - die."
Gloucestershire Health and Care and Gloucestershire Hospitals NHS Foundation Trusts said: "We have already taken positive action to address the ombudsman's recommendations.
"Whilst, sadly, we cannot change the outcome, we are committed to learning from Erica's tragic death. We have extended an unreserved apology to Erica's family."