Twice, before I fall into deep sleep, I had experience hearing someone talking to me or some footsteps but I couldn't move. Its feels kinda scary cause these symptoms would direct me to believe something not suppose to be there was there. I tried to fight to move but I just felt paralyzed the few times.
Hence, I went to research on it and it is explained that when a person sleeps, his brain will sends signals to inhibit any muscle contraction. If we comes into consciousness before the brain sends signals to activate muscle contraction, he cannot move his body, and consequently, become "paralyzed".

Scary experience but with a cool explanation even though it sounds like the signal is moving slowly in my brain! Hahaha!