The trust which runs mental health services in Norfolk and Suffolk has apologised after an inquest found that neglect contributed to a patient's death.
Neil Jewell, 42, died in 2014 after a series of failures, the inquest said.
He had paranoid schizophrenia and was not properly monitored after being given a tranquiliser.
The Norfolk and Suffolk Foundation Trust (NSFT) said it had already identified changes in practice.
Mr Jewell had lived independently at his home in north Norfolk but, in early 2014, ran out of medication and became agitated.
As the nearest specialist mental health bed was in London he was placed in a care home in Norfolk but, as his condition deteriorated, staff could not cope with his behaviour.
Following a transfer to a mental health unit in Ipswich, the inquest was told trust staff did not adequately monitor his vital signs after he received tranquilisers.
When, on 12 January 2014, Mr Jewell was found head down and foaming at the mouth, the inquest was told an agency worker did not know where to find the oxygen in the unit so valuable time was lost while trying to resuscitate him.
Five days later he was diagnosed with brain damage and his life support machine was switched off.
The inquest jury found Mr Jewell died from complications following a cardiac arrest caused by him not being able to breathe and the effects of sedative drugs used in his "rapid tranquilisation to which neglect contributed".
NSFT chief executive Michael Scott previously said: "Since his [Mr Jewell's] death, our trust has ensured that patients based in the community have a named mental health professional or duty worker co-ordinating their care, to offer greater support."
Mr Jewell's family said in a statement: "The evidence during this inquest clearly points to a catalogue of missed opportunities, poor decision making, inadequate record keeping and routine disregard for policies."