I cannot tell you what causes this, whether or not it is truly alien abduction, or something else.
I can say that I have definitely experienced this, and it is terrifying. I experienced it once every few years until I was in my 30's, married, and when I awoke at 3 in the morning and tried to wake my husband and couldn't I called my parents. Yep, 30's, married, and I called Mommy and Daddy!
Dad came to get me.
Mom had an audio tape ready in the tape-player of someone reading from the bible and a bed ready for me on her apartement floor.
She stayed awake all the rest of the night for me praying. I know she did.