An 80-year-old man's "obsessive worrying" could be evidence of abnormal mental functioning when he killed his wife, a jury has heard.
Robert Lewis stabbed Janet Lewis, 76, as she slept at their home in Hullbridge, Essex, on 1 September 2019, and then attempted to kill himself.
He was "obsessed" with the idea he had dementia and that his wife would suffer a stroke, his trial has heard.
He denies murder and has not given evidence at Chelmsford Crown Court.
Fatal neck wound
The trial has heard Mrs Lewis, the defendant's wife of more than 50 years, was attacked at about midnight with kitchen knives and a club.
Believing he had killed her, Mr Lewis then attempted to stab himself on the landing before attaching a noose to a rafter in the loft.
His injured wife made it out onto the landing where Mr Lewis delivered a final stab wound to her neck.
He was found with a broken hip at the bottom of the stairs - the noose having broken - when their daughter and son-in-law arrived to take them out for lunch.
In police interview he said he had no recollection of events.
'Something wrong in his head'
In her closing speech for the defence, Alison Gurden said the jury should consider a diminished responsibility defence for Mr Lewis, who is now 82.
His family had "grave concerns" over his trouble sleeping, loss of appetite and obsessive worrying and he was placed on a "starter dose" for anxiety and depression, the court heard.
"Mr Lewis was concerned himself [and told his son Paul] 'there's something wrong in his head but he didn't know what it was'," said Ms Gurden.
She told the jury it could ask whether Mr Lewis's obsession with the boiler breaking - including while in prison - was evidence of abnormal mental functioning and impaired judgement.
He was also worried that Mrs Lewis would suffer a stroke, without cause, and that she would go into a care home at a cost of £800 a day.
Psychiatrist Dr Hugh Series, who appeared for the defence, said Mr Lewis had abnormal mental functioning, but he was not sure if this would have substantially impaired his conduct.
In his closing speech, prosecutor Andrew Jackson said Mr Lewis did not have severe depression.
"He wouldn't have been going out for a pub lunch, which he would've done had he not chosen to kill his wife 12 hours earlier," he said.