I've had this problem my whole life up until a few weeks ago. I was preparing for my final school exams when I had multiple performances coming up and didn't feel ready at all. I thought that instead of worrying about hitting wrong notes all the time, I'd practice my pieces with over-the-top emotion, exaggerating every litttle hand movement so it was ridiculous. I played everything with too much rubato and played whatever dynamics I felt like, not completely disregarding what was written, but just exploiting it I guess.
I tried on purpose to make it ridiculously showy with expression. Obviously this isn't the best way to do it in a proper performance, because it has to have TRUE emotion, not staged, but practising this way helped me to feel more free in my actual exams, and it worked. I wasn't worrying about the right notes because I felt more confident in giving getting the right impression and expression out of the music.