The partner had then texted that he would phone police, and Gill saw that text "and interrogated her about that".
Judge Morris said Gill had then pulled a 20cm carving knife from a drawer, and "having got that, you told her you were going to kill her and yourself".
Gill's mother had then screamed for help, after which he "forced her to the floor and forced (his) knee on to her chest", and covered her mouth and nose with his hand so she could not breathe.
He had made her promise she would not scream, before letting her back up. "She got up and wrapped a towel around her neck - such was her concern that her throat would be cut," the judge said.
Gill had then phoned his mother's partner and told him that if the police were called, "you would stab her in the face".
The police had arrived and Gill told them to leave, but his mother "managed to mouth help".
Gill had then presented his knife to police, who retreated.
He had put the knife to his mother's throat and "marched her to the window and told police (he) would kill her if they didn't leave".
Gill had gone to a cabinet and consumed some medicines.
The police had phoned him and Gill told them "if they did not go, there would be a massacre and a bloodbath".
Eventually Gill had agreed to leave the property unarmed.
Judge Morris said Gill's mother had suffered abrasions to her mouth and nose "with the partial asphyxiation that you inflicted", as well as bruised ribs.
"She had a belief that you were going to kill her, and she had never been so traumatised in her life." Six to eight weeks later, the woman had suffered a stroke.
The judge said without medical evidence she could not hold Gill responsible for the stroke, but "no doubt the stress contributed to that".
She said the kidnapping was "a sustained action by you, over a period of well more than an hour".
Judge Morris said she "can't take into account any effect of drugs" Gill had taken, but could take into account other factors, discussion of which she suppressed, in giving a sentence she called "mercifully low".
The judge said she accepted Gill's guilty plea was "an expression of geunine remorse".