Sleep Paralysis is a "disorder" I guess you could say characterized by not being able to move your body even though your brain is conscious. After a bit of research I found out that it happens because when you sleep, your brain becomes disconnected with your body for a while to let the muscles relax and so that it's activity during R.E.M (Rapid Eye Movement) does not disturb the body's rest. Sometimes though, your brain can become disconnected from your body a little too early, or doesn't re-connect with your body in time; thus causing sleep paralysis shortly before or after sleeping.

Many people also experience hallucinations of various kinds during sleep paralysis that make the experience far, far worse. I personally have never had the hallucinations but I can only imagine how frightening it must be since the sleep paralysis is pretty scary in and of itself.

For me, it usually always happens right after I wake up. I don't think I've ever gotten sleep paralysis right before I've fallen asleep. It really is frightening though and most people can't understand it until they have experienced it. What's worse for me though, and I'm sure it's happened to many people, is that it happens multiple times when it does. What I mean by this is, I wake up with sleep paralysis, and then when I finally snap out of it I'm still drowsy and sort of half asleep. Before I know it, I fall back into sleep paralysis and have to go through the experience all over again. It happens multiple times with cycles of what I like to call limbo: The state in-between sleep paralysis phases. In this state your still pretty much half asleep and so physically can't wake up. You're still at a very high chance of getting a sleep paralysis "attack" but you're pretty helpless at this point. You're too drowsy to actually wake up but relatively conscious on the inside, awaiting your next bout of sleep paralysis.