A loving son was mentally ill when he killed his elderly mother intending "to shut her up so she couldn't say anything anymore or bother him for the rest of his life", a judge has been told.
Boutros Mouawad was suffering a substantial impairment by abnormality of the mind related to his inability to control himself while he was "manic" during a bipolar episode, according to two psychiatrists.
They gave evidence in the District Court in Wollongong on Wednesday at the sentence hearing for the 57-year-old Illawarra man, who had been on a disability pension.
Mouawad, who was originally charged with murder, pleaded guilty to the manslaughter of Helen Mouawad, 76, at their Woonona home in February 2019.
The agreed facts state that Mouawad had argued with his mother before striking her with a plank and leaving the house to attend an RSL club.
When he returned, he didn't know whether she was dead or alive so he struck her again because he wanted to make sure she was dead "to shut her up so she couldn't say anything anymore or bother him for the rest of his life".
Judge Christopher O'Brien was told the pair previously had a loving relationship.
Mouawad had last taken medication about seven years before the attack and he hadn't seen a medical professional for 10 years.
He will be sentenced on October 16.