Sleep Paralysis
Sleep Paralysis can be petrifying for the large number of people out there who have experienced it. You wake up, your eyes are open you can see, you are fully conscious but unable to move - hence the paralysis bit. Sleep Paralysis can cause Hallucinations can occur which make the whole thing even more scary. I can not imagine how scary this must be, laying there frightened and unable to move. I found this clip of someone experiencing Sleep Paralysis - it looks really hard to bear.
I had heard of night terrors as one of my boys gets these in the night. He can get really upset in his sleep and I often have to go into him and try to comfort him. We have been told if possible not to wake him. Unless of course he gets too upset.