Since everyone is different, some are more open than others to psychic abilities, etc., I would think some people have certain parts of thier energy centers more open than others which allows them to leave their body at will.
I am one of those who have no skills whatsoever to astral project. I think I'm far too grounded to this earth to allow this, but I wish I could. Not to mention, that if there is any truth to astology-- I am soo overly grounded, that it even shows in my moon and sun signs (Taurus sun sign with Capricorn moon sign--the most Earthy grounded signs in the Zodiac!)
What you may want to do in regards to the fear factor relating to this.. Why don't you pray for God's shield of protection even before going to bed?
Ask that if you get that sensation again, that it would be used for your highest good, and if you would be permitted to leave your body, that it would be used for something constructive and not for selfish reasons. And above All, that God would protect you.
I read a person's testimony of someone who astral projects, and actually met God that way.. Also they are being used to help souls who are stuck on the astral planes to go to the Light. You never know if the reason you may have this "talent" may be for use for God's will in some way like that.