You could keep the person hospitalized and trapped, and there would be multiple ways you can perform this:
You could convince the target and staff that they are ill with whatever you choose (you can will pain into existence if you really believe something is hurting you, you can also use your memory manipulation to infect/poison/drug the victim, while keeping your story perfectly unaffected)
You could also put them in critical condition, and maintain that by repeatedly harming the person, or by forcing incorrect care by controlling staff
There is always better options, you could just mind control somebody into a wood chipper, or torture them in another way, but going for less extreme options creates some very interesting scenarios
Make someone believe they are/were raised by an animal.
Make someone forget muscle memory, forget how to walk or pick up tools.
Make someone kill/torture their loved ones or themselves, with complete awareness but inability to control their actions
Make someone kill their loved ones then make them believe a friend did it
Make someone forget imagery/characteristics of every specific thing but not their experiences or relationships with said things. They would have a basic summary of everyone and everything they know but no way of identifying them
(e.g. they would see every person as just a stranger but they would know they had significant people in their life and what things they did with them)
surround them in an invisble box, everytime they leave this box their consciousness instantly starts to fade away and the subconsciously move back in the box
Cause a select few people to commit very heinous crimes and then make the law enforcement endorse it leading to national unrest then cause the leader of the country to make a ton of legal stuff illegal like walking in a park and give big sentences for light stuff then mind control someone to catch the leaders body and watch the country fall into anarchy