Anxiety, low blood sugar, too much coffee or tea, overactive thyroid, Parkinson's disease, and some medications are some of the things that can cause this. Some neurological conditions are cause uncontrollable shaking of the hands and feet, so it would be best if you talk to a doctor about this for proper diagnosis.
Oh. You may have a neurological condition that needs IMMEDIATE diagnosis and treatment. Not knowing your age, I can't suggest any possible causes with confidence, but none of the likely pathologies can wait. Get thee to a GP yesterday - if not sooner.