Sleep Paralysis

Every once in a while I'll have this strange experience while trying to fall asleep (more often when I wake up in the middle of the night and i try to fall back asleep). I'll close my eyes and after a minute or so, I won't be able to open them, I won't even be able to move, but I'm still conscious. Sometimes I'll hear strange electronic sounds. I get a little scared whenever it happens, and if I want to come out of it I have to try really hard to get up, like jolt my eyes open and jump out of bed. This has been happening to me as long as I can remember, and I've kind of gotten used to it. I just wanted to know if anyone else experiences something like this, or has read about anything that fits that description. Is there some chemical in your brain that could cause this, or could i have some sort of fatal neurological disorder? Any information would be welcome.