Same here, this is one of my biggest problems. Sometimes I get really anxious about talking to someone a few metres aways because im worried my voice won't carry. If there is more than one person in the vicinity it becomes harder for me to speak out loud for fear of having everyone hear what I am saying. I worry about saying something stupid, my voice not carrying, talking to fast, not being able to formulate a sentence, stuttering, being unable to control my facial expressions...the list goes on. It may also have something to do with the fact that I analyze what Iam going to say before I say it, and my mind is always trying to get what comes out of my mouth perfect so as not to bring too much unwanted attention to myself or a negative reaction from the other person.
Additionally if I fear something is going to go wrong, or if something does go wrong, the anxiety can just overwhelm me mid sentence and my mind goes completely blank.