Rajesh Pannu, 32, who was not suffering from a relapse at the time, had pleaded guilty in July to three of the five charges of beating up his mother in the family apartment.
Rajesh threw away his mother Narindar Kaur's walking frame accusing her of making noise when he was watching television on November 19, 2014.
He hit her on the forehead with a plastic mug, threatened to kill her, and used a broom-stick to beat her until it broke.
When he saw the bleeding mother painfully walked to her bedroom without the walking frame, Rajesh became more angrier and continued his "vicious and merciless" assault on the old lady.
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He slashed her right forearm with a knife twice and poured hot water on her. Later when he found her laying on the toilet floor, he called for an ambulance.
Sunil Sudheesan from the Association of Criminal Lawyers of Singapore said "My client accepts responsibility for his actions. But he also asked the court to enclose a psychiatric report in the warrant of commitment to ensure Rajesh gets full treatment in prison."
The prosecution withdrew canning as a punishment citing Rajesh's condition. For causing grievous hurt with a heated substance, the maximum penalty is 15 years' jail and fine or canning.