speak loudly and clearly

For whatever reason, when I’m in an official type setting, my voice becomes quieter and I will often trail off on the end of sentences. I simply cannot complete them and my voice goes very wispy until eventually no sound comes out. I don’t know why this happens because I don’t get nervous in such situations anymore, after having been exposed to them in college. Even during presentations this can sometimes happen, although my thesis presentation went very well and I don’t recall ever having this problem, which one would not expect, given it was probably the single biggest accomplishment in my college career :) I plan on trying to eliminate this problem because I know that if it happens in interviews, it will definitely hurt me. Just wish I knew why it happened D: