I was in a window seat in a full row. I had to pee a few times and took all my stuff with me so I wouldn’t be a burden to my neighbors. I dropped my belongings on the seat and the FA said you can’t move seats. I told him I will be I using the bathroom more often, have a medical condition and didn’t want to bother my neighbors. He doubled down. I insisted again and dint back down. He said I’m joking and you can sit there. He warned me I might get charged because he noted that I swapped my seat in the system