What you're experiencing is actually a fairly common phenomenon. I have had this experience myself a few times but I wasn't paralysed at the time so it wouldn't have been as scary as your experience. All I can suggest is that you prime yourself not to be scared and to realise it's only HH (Hypnagogic Hallucination). Keep reminding yourself throughout the day and right before you go to sleep at night that if you experience this again it it not real