Sleep paralysis always terrified me. Even when I expected to have an episode, I was afraid of the confrontation. My fear was such that I went without sleep for several days, I used the Bible and crosses to keep them away and even slept in other places to stop the episodes.
You are awake in your dream state. This means that whilst your physical body is immobile, your energetic body has the ability to engage the experience. So whilst sleeping you try to speak, but the physical bodily muscles that create sound can not, as they are relaxed as you sleep.
Making grunting noises whilst trying to force yourself awake helps. As the experience seems real, you expect to be able to shout out, but the body does not allow it. I guess that that’s when you realise the conflict between reality and dream state and begin to panic.