'self hypnosis' or biofeedback may be helpful in some people.
Have you ever tried self hypnosis to help you with the problem? It helps a lot,I have found with a wide variety of problems. You can correct a lot of health and mental health problems with self hypnosis.
A family practice doctor or internist may be willing to prescribe a beta-blocker for this occasion and purpose. I would not advise tranqlizers because you want to be there and remember your graduation. There are also many relaxation techniques you can use - many books and clubs (e.g. toastmasters) deal with this common complaint.