Did some quick homework for u:
Deep, slow breaths through your nose and out your mouth with regulate your heart rate, and help to calm you down.
One way to do this is to pretend your hand is a statue. You can stay as still as you can, or you can practice by having someone stand right next to you or watch you to see if it moves.
Another way to do it is to keep a rock on it so you can keep it up to see if it does not move.
Also try doing this:hold your arm straight and pretend you are holding something. P.S.,after a while,you will feel your hand coming down.
Also man go see the docs, could be nething from high stress, aniexty, glucose levels, to much caffeine, neurological disorder many things m8.