This is a very irrational feeling which can be combated by reminding yourself about the logic of what's going on. Why get worked up over something you can't control. It's like you might win, you might lose, maybe even a little of column A, and a little of column B.
You need to accept what you are getting yourself into, and then accept you might lose a bunch of money and their is literally nothing you can do about it.
That should help minimize the heart rate problems.