What's the WORST that could happen? You could say something dumb, be mocked, and have your silly comment referenced for the rest of the class session...or even the rest of the semester! Alternately, you could say nothing at all, petrified from fear, and either pass out or vomit. Then, your nearby colleagues will need to assist you with your medical condition while class marches on.
In either mortifying scenario, you'd still proceed with your life, and graduate, and hit the workforce, and no one would be the wiser. :-)
**
Basically, the "worst" that could happen is just that you won't perform well, and you'll internally beat yourself up, and then you'll move on and feel less scared the next time (and the next, and the next).
I think a lot of the fear that comes from the Socratic method is just fear of public speaking, fear of being judged, fear of failure. If you're terribly worried about public speaking, you can overcome your fears through Toastmasters, other public speaking or outreach programs, or confidence/leadership efforts.
One simple, expedient way to rip the Bandaid off: volunteer. Yep. Raise your hand and ask a question, or volunteer an answer. Or go up after class and talk to the professor. That eliminates the mystery and the suspense.
It helps to remind yourself that it won't make a difference in two years. Hell, it's unlikely to make an impact in 2 weeks. So, if you can conquer your nerves here, you can redirect that energy towards something else.
Don't worry -- this, too, shall pass! And when it does, you'll be a bit stronger for it.