Hey Kelly,
You might have specific social anxiety disorder, where your body physiologically reacts to certain stimuli by drastically increasing your heart rate and shallowing your breath, kind of like a panic attack. Probably in circumstances where you have to speak up with a formal expectation to do so and in formal settings like classrooms.
I know I have had a moderate case of this since I can remember, but I didn't talk to a psychiatrist until only two weeks ago. And aside from prescribing drugs, which I didn't want, the key to relax this condition, is like other people said by desensitizing the person through progressive exposure to it. It's just like another phobia I guess...