I had similar experiences when i was a kid.Mine was after id just fallen asleep (But i knew i was sleepining).I ve had them about 5 times in my life.I was 15 when i last had this experience, Im 33 now...so i guess it`ll pass...I agree its a teriffying experience.mine used to be accompanied by a horrid screeching noise.I assure you it was the worst soundf in the universe.I remember trying to wake up (I had this teribble feeling i was being sucked into somthing horrible).The worst part was, even after i woke up if i tried to go back to sleep immediately the expeience would continue from where it had stopped.Dont worry, itll pass as u get older.

Sometimes out of body experiences are frightening. Usually it is caused by being startled, a noise in the house for example, and we try to get back in our body quickly.  Sometimes that is hard to do and you not only feel frightened but maybe have a hard time catching your breath or feel like something heavy is laying on you.  I believe that everyone has regular out of body experiences.  It's the bad experiences we remember.   I ask in prayer and meditation every night that if I have to go out that I return safely and gently.  Sometimes when we get enough sleep but still feel tired it's because we're traveling.  I ask that I stay in my body for a few nights to feel rested.  Although, it can be scary at times, I don't know of anyone who every died from out of body.   The worst thing you can do is panic. Relax and you should fall right back into your body.  Get up and walk around the house for a few minutes before going back to sleep.

Blessings

it happened to me once last year

I remember I fell asleep quickly because I was very tired, and though I knew I was already sleeping I saw everything around me as if I was awake. I saw the walls of my room, the ceiling and the door in front of my bed and I knew I had my eyes closed. Then I started to rise in a slowly motion way. I felt like floating above my body, it was very odd but it felt really nice at the same time. I was afraid so I tried to wake up and I did.