I tried to submit my reply quickly, but my internet connection decided to just die quickly.
So, I had the same problem as well(still sort of have), and people have actually told me that what I say, was almost always incomprehensible. It affected me really deeply, as I remember getting thoughts like:
'You're going to do worse this time'
'You're going to be inaudible anyway',
whenever I tried to speak up. But I eventually learned to be more confident - even if it meant that my anxiety would get affected. It can be really hard to deal with the anxiety at first, but all you have to do, is to try and distance yourself from the self-consciousness which might be the prime cause of your panic.
Adopt a confident body language - one that will allow you to stay in a comfortable state of mind. I would highly encourage you to try your best to take gradual steps to sound more assertive and confident. I know it can sound really hard to just listen to all the theory, as it's really difficult when it comes to practise. But I can relate to the experience, and I must confess that the only way to counter this is by taking a more positive view of yourself, and to be more confident in yourself.
For beginners, try speaking your mind without over-thinking how your friends/ colleagues might judge you. Begin like that, and slowly raise the difficulty. I'm sure you will do better eventually. Good luck.