This happened a few months ago. I had this weird feeling i was going to die, and then everything went black and it felt like i was flying backwards 
, then after a few seconds of that, i started going down, and all of a sudden, i opened my eyes, except they were already open which was very weird. Can someone please tell me what happened, it was very very scary 
after it happened, but the next day i realized it was pretty fun, it felt faster than a rollercoaster.
Hmm not too sure to tell you the truth… could have been a blackout, which is just a lack or iron in your diet causing at random times everything around you to fade to black, you feel dizzy and almost faint, then your vision returns to normal.
It seems you forgot to tell the most important thing. 
Were you completely awake or where you lying in bed? As you said you opened your eyes, I suppose you were in bed.
In this case, it’s the feeling you can have when you just fall asleep (and generally lose consciousness). Some people could say it was the beginning of an OBE (because of the flying backwards feeling). I’m suprised by the fact that you say your eyes were already open. This last point looks like a false awakening. 
About the feeling you were going to die, it’s a point that, in my knowledge, stays unclear. This happens too during SP episodes. It’s what is called a panic attack. I don’t know why we have this when our state of consciousness get altered.
If it happened during waking life, it’s like a fainting. The symptoms are quite the same than falling asleep indeed, but quicker. This may happen too in some rare cases of unvoluntary altered states of consciousness, for instance when very tired or stressed. This happened to my aunt, she was discussing with people when she sort of lost consciousness during one second and she saw herself from another point of view. 
i was laying in bed and it freaked me out, i expected it to happen, it was so weird, but i do things with out realizing it sometimes. I think I was doing WILD without trying and i actually started to go into a dream, but i got so freaked out, i woke up. Thx for everyones posting, but if anyone else has any opinion whatsoever, i’d love to hear it, bc i’m still a little confused lol.