Maybe you have something going on psychologically? Like something you're holding in, something you want to tell someone but haven't and you're dreams are telling you that you need to get it out. Parents are someone to go to for safety, maybe their sitting and watching is a sign that they can't help you anymore and you have to speak on your own? Just thoughts.
It could also be sleep paralysis, I've experienced this before. Are you any bit awake when u can't speak and feel held down?