It's been a while since it last happened but I have experienced this quite a few times over the years. But I always thought it was the absolute fear I was feeling that was paralyzing me. I could swear someone is there, my heart feels like it's going to beat out of my chest and I can't move which terrifies me even more. A few times I've also experienced the feeling that someone had touched me.
Show me the right path, O Lord; point out the road for me to follow. Lead me by Your truth and teach me, for You are a God who saves me. All day long I put my hope in You. (Psalm 25: 4-5)
"For God so loved the world that He gave His only son, that whoever believes in Him shall not perish but have eternal life." (John 3:16)