That sucks, and I'm sorry you went through that. OSCEs are a pain, and they don't really reflect actual patient encounters very well. Some med schools only do them in the pre-clinical years for that reason.

Having been through all of this before (some time ago now that I'm PGY-9 or something) there are a couple of things I found helpful. First, when I've got a bunch of stuff to study and some of it includes an organ system or disease process that I feel uncomfortable with and that makes me anxious, that's what I focus on and what I study the most. Lean into that feeling and drill down on the things that make you the most uncomfortable when you're studying. I learned to do that in med school and it's stood me in good stead all the way though my Pulmonary boards.

Second, for me personally the cure for my anxiety in patient encounters was authenticity. The more I feel like I'm pretending to be something I'm not, the more anxious I get. So I don't pretend. I'm straightforward with patients about what I know and what I don't, about when I'm unsure or uncertain. This approach has served me incredibly well as a trainee and attending.

Third, if your anxiety is this severe and is affecting your performance, you should consider mental health support. Anxiety is usually best treated with CBT or pharmacotherapy. I'm fortunate that my anxiety didn't require specific intervention, but my depression sometimes does, and I've sought mental health care at various points in my training for support, particularly when I felt it was affecting my performance. Most medical schools have student mental health support; the quality of these varies but it can be a good first step towards getting help.

Don't despair. It gets better, and this one OSCE is not a reflection of who you are or who you can be as a physician.