The victim suffered stiffness to her neck and shoulders and also had swelling.
Several weeks later her attacker, Frances Agwu, described as a large woman and six-feet tall, grabbed a plastic kitchen knife and stabbed another female nursing assistant in the stomach.
Her second victim suffered a red mark and distress at being assaulted by a patient she had previously worked well with, Nottingham Crown Court was told.
Both offences of common assault, on 5th May and 18th August last year, happened without warning.
On the first occasion the nursing assistant, working a night shift, completed her round at 10pm and went to sit next to Agwu in the day room.
Out of the blue Agwu attacked her, grunting and squeezing hard, said Abi Joyce, prosecuting.
Other patients shouted at her to stop before staff pulled her away and took her to the floor.
On the second occasion Agwu was at a serving hatch in the dining room when she grabbed a knife and turned on her victim. Other staff intervened and the knife was pulled from her grasp.
A doctor told the court that Agwu, who had two previous cautions for common assault, suffered from a mental disorder and it was appropriate for her to be further detained for treatment.
Agwu was made the subject of a hospital order for an unlimited period.