Medical research suggests that these state causes horrific figures to manifest because they are a product of strong sudden anxiety caused by a synergy of factors like being completely paralysed, having no freaking idea of what's going on and all this leads to a kind of panic attack ( this is what happened to me, infact I thought I had a panic attack). The symptoms of sleep paralysys are very similar to a panic attack, tachycardia, hyper or hypo ventilation, fear of dying. All this working together isn't pleasant, it's very disturbing, that's why you don't have teddy bears or mini ponys dancing in your bredroom but evil presences. When you know what's going on and don't panic you don't necessarily have these unpleasant visitors, like in SP during a WILD. Well that's at least my rational explanation to the phenomenon but anyone can see it as he/she prefers. One thing can be accepted by everyone though.... when it happens it's fu%&*ng scary!!!!