One of the men convicted of hacking Fusilier Lee Rigby to death punched a nurse in the jaw in Broadmoor hospital after being asked to turn down the TV volume.
Reading Crown Court heard Michael Adebowale, 28, is spending another period at the secure hospital and is suffering from "chronic paranoid schizophrenia".
He pleaded guilty to punching healthcare assistant Jason Taplin while being held in Broadmoor on July 20 last year.
He claimed to have been hearing voices telling him to attack Mr Taplin before the incident.
After denying a more serious charge of inflicting grievous bodily harm, Adebowale admitted an alternative charge of assault causing actual bodily harm at the court on Monday.
Adebowale was given a eight-month prison sentence by Mr Justice Jay which will be served after his 45-year minimum term for the murder of Fusilier Lee Rigby in Woolwich in south London in 2013.
He is currently serving his sentence at Broadmoor, where he has spent three periods since his conviction, and is expected to stay there for the next few years to be treated for paranoid schizophrenia.
Mr Justice Jay said: "There is only one previous conviction but it is a significant one."
Adebowale and Michael Adebolajo ran over the 25-year-old soldier close to Woolwich barracks in May 2013 before stabbing him to death in broad daylight.
The father of one died as a result of multiple cut and stab wounds after the attack fuelled by Adebowale and Adebolajo's extremist beliefs described as a "betrayal of Islam" at their murder trial in 2014.
Adebowale is expected to spend the next "five or 10 years" in Broadmoor, the court heard.
Adebowale, who has changed his name by deed poll to Ismaail Kuti, appeared via video link from the secure hospital for the hearing.
Sarah Whitehouse QC, prosecuting, said that Adebowale punched the nurse in the jaw during the incident in a day room of the hospital.
Ms Whitehouse said the attack was triggered after Adebowale was asked to turn down the volume of a television he was playing music through.
Adebowale was "plainly upset and annoyed" by the request, she added.
CCTV footage shown in court showed Adebowale approaching Mr Taplin before punching him and knocking him to the ground.
Mr Taplin was taken to hospital and examined. After it was disputed whether the injury had broken the bone, Adebowale was able to plead guilty to the lesser charge and avoid a trial.
Sasha Wass QC, mitigating, told the court Adebowale admitted hitting Mr Taplin when frustrated but did not break the bone.
She said: "He accepted that he struck a blow, one blow, but he did not or he would not accept that he broke the jaw."
Ms Wass added that Adebowale suffers from "chronic paranoid schizophrenia" and was hearing voices telling him to attack Mr Taplin before the incident.
She said: "He is clearly unwell, he clearly had a lapse in self control and he regained his self control and he immediately showed his remorse by writing a letter to Mr Taplin.
"His medication was not sufficient to deal with the psychotic state he experienced on July 20 of last year and as a result of that state he administered the blow."
Mr Justice Jay said his sentencing decision will not significantly affect the 28-year-old's immediate future.
"He has got another 39 or 40 years to go and may in fact never leave Broadmoor," he said.
Passing down the eight-month sentence, Mr Justice Jay said: "There was a dispute between you and Mr Taplin.
"I have absolutely no doubt Mr Taplin was in the right and you were in the wrong.
"What the CCTV clearly shows, that while Mr Taplin was in conversation, no doubt of work-related matters, you approached him from his left and on my interpretation of the evidence you delivered one hard blow.
"It was a combination of the illness and the stress that was working on your mind that I feel was another factor in your case."
Mr Justice Jay accepted that Adebowale had heard voices before the attack.
"The injury would have been very painful for a period of time, possibly a considerable period of time and I hope you sincerely regret that."
After serving his life sentence, Adebowale will serve half of the eight-month prison sentence before being released on licence.
A further count of inflicting grievous bodily harm will lie on file.
Adebowale was born in the UK, but has Nigerian parents.
In April this year he was said to be desperate to get out of HMP Wakefield, where he is serving a life sentence, and move to a Nigerian Jail.
An insider told The Sun: "Michael hates Wakefield. It’s stuffed full of lags who see him as a top target."
Lee's mum Lyn said: "He should serve his sentence here and not try to exploit the law for a cushier life."
In June we told how a drugs baron who was jailed for orchestrating a coke and cannabis distribution network was caught up in a brawl with the killers when they were in high security nick Belmarsh.
Underworld kingpin John Anslow – the mobster whose jail escape made national headlines - had a neighbouring cell near the pair.
The fight was allegedly the culmination of simmering bad blood between him and the terrorists after he became increasingly agitated over the pair’s loud, all night conversations.
The Black Country drugs baron, who is serving a 22 year sentence, got the better of the brawl, his father, John Senior, claimed.
His dad said: "All night and all day they were shouting. One each side of him. One tried to put it on him and came off worst.
"John got him on the floor and was throwing punches before the screws pulled him off. He gave it to him.
"He stood his ground and had a go back."
