the satan, could be your boss, or authority. inability to speak could be something that took over the control of you. say, for examples, if you were in abusive relationship and your partner wouldn't let you speak.
your parents, your friends?
Could mean anything. Presumably there's something you're scared of and you don't know how to deal with it... but that describes just about everyone on the planet.
When I was a kid i dreamed every night that a cartoon Satan was chasing me with a Chainsaw.