Keith Lisle and his girlfriend of 13 years had been out for drinks on January 1 then tucked into a takeaway when they got back to her home.
Newcastle Crown Court heard when the woman went upstairs to get changed after she dropped some food on her clothing Lisle followed and launched a shocking attack.
Prosecutor Omar Ahmad told the court: "She described spilling her takeaway on her and going upstairs to change.
"Next thing she remembers is lying on her bed in her bedroom with him standing over her, punching her to the left side of her body.
"She doesn't know which fist he was using or how many times.
"She is unsure how long the attack lasted but states she possibly had been unconscious during part of it.
"She remembers crying and it caused the defendant to stop and said 'what are you crying for, those are false tears'.
"He went downstairs, got his belongings and left."
The court heard Lisle took his victim's keys when he left, which left her locked inside the house.
She called for help from a friend who then confronted Lisle and got the key back.
Lisle told the friend he could not remember what happened but then admitted he had followed the victim to her bedroom, where he "exploded" and attacked her.
In a victim statement, the woman, who had been left with a swollen and bruised face, said: "I am in total disbelief a man who supposedly loved me could assault me to this degree.
"I keep replaying things in my mind to establish whether it was me who did anything wrong or said anything wrong but I know I didn't do anything to upset him.
"I didn't even know he was in the bedroom, he just appeared and frightened me.
"I didn't deserve to be assaulted in my own home. I no longer want to be in a relationship with Keith Lisle and will sever all contact."
Lisle, 52, of Beatrice Terrace, Ashington, admitted assault.
Shaun Routledge, defending, said the violence was "impulsive, spontaneous" and there had been no similar behaviour in the past.
Mr Routledge said Lisle has medical problems and is due to go to hospital for treatment.
Judge Christopher Prince sentenced Lisle to 16 months behind bars.
The judge told him: "This was a most unpleasant assault on her.
"All she had done was go out with you that day. She said you and she had had a nice time.
"The pair of you had been enjoying yourselves and enjoying a meal when you got home and out of the blue you just set about her."