Whoever bumped this thread back up, thanks - have spent a good few hours going through all the links, some seriously creepy and weird stuff in this world.
Like a couple of previous posters mentioned, I have occasionally had the 'sleep paralysis' thing, but unfortunately for me I get the one with the 'Terrifying Hallucinations' which in my experiences always feel like I am being pulled at and clawed at by someone/something. Knowing that this is a well documented effect does not alter the fact it is an absolutely terrifying mind f**k of an experience, and I generally have to stay up all night with the lights on afterwards.
http://en.wikipedia.org/wiki/Sleep_paralysis