I think the only way to get over this is to get called on.
Once it happens a couple of times, you realize that you survived afterwards. Also, if you haven't been called on yet, take a risk and raise your hand to answer a question. Put yourself out there. It can be terrifying, but I found that until you've gone through it a couple of times, it's still an unknown terror.
Also try to keep in mind that class performance has little to no effect on your grade. That doesn't really help, but it can't hurt.