Daniel Hampton's father, George, had cared for his son, but is now poorly himself with Parkinson's, Preston Crown Court was told.
He was left with eight broken ribs, and swelling and cuts all over his body after his son suffered an episode and subjected him to a sustained attack, which ended in him pushing the him out of their caravan, causing him to fall.
The court heard on November 24, the defendant kept calling his father 'Peter', and when the elderly man tried to correct him he became angry.
The defendant was suffering a delusion that his father was someone called Peter who was spying on him.
He punched him to the face five times, kneed him in the chin, and kicked his chest three times.
The defendant continued to be agitated all day.
At 10pm police attended the caravan, on Riverside Caravan Park in Banks, near Preston, as a result of a welfare concerns from social services.
It followed a suicide attempt by the defendant days earlier..
But when they saw Mr Hampton senior's injuries he told them he had fallen.
The following day, Mr Hampton senior noticed his son continued to be agitated.
He then demanded his father left the caravan to buy him cigarettes, and was seen by several neighbours to push his father down the steps - though the victim says he fell.
Mr Hampton senior suffered serious injuries, and his son was sectioned on November 26.
In a heartbreaking statement he said: "I've always loved Daniel but I was scared."
Daniel Hampton pleaded guilty to wounding with intent, and a further two counts of assaulting a paramedic in A and E at Southport Hospital on November 14.
The workers had transported him to hospital after he suffered a fractured elbow during an attempt to take his own life.
Recorder Tania Griffiths QC accepted he was "acutely mentally ill" at the time of the incidents.
She added: " I accept you love your father and he loves you, but what you did next was horrifying and inexcusable.
"He says had you not been handicapped by the cast on your arm you would have killed him."
She imposed a hospital order for treatment of bipolar affective disorder.