Haven't seen one of these mysterious hallucinations? Try this.
Stay up for 2 days straight without any sleep. Eventually your brain will release a natural drug into your bloodstream (forget what the drug was called) that basically makes you hallucinate like crazy. I stayed up for 3 days straight once with a friend of mine, and kept seeing full figured gray colored people running through my house. Sometimes I would just go insane and chase after them. It's pretty fun but also pretty scary. Then you get the occasional spots of rainbow here and there. Basically your brain is telling you "Ack, I'm tiiiiired, let's go to sleeeep!"
Ive experianced some similar things during hypnogogic sleep (i think thats what they call it)
Once I woke quickly in bed and stared at my trousers hanging over my chair for a few minutes. I was half-asleep and i noticed the legs of my trousers started to curl up. I jumped up and they were back to normal.
Annnd one morning, my alarm was going off and my mum comes in to turn it off. She picks up my alarm clock and im barely awake and i turn to my shelf to turn it off. I say to my mum "no no wait its not that ill get it" I was looking a minature black bag with legs (yes) running around my shelf ringing. I hadnt taken anything.
Another example - i hate spiders. Other night I woke and on returning from the bathroom and getting back into bed i saw a spider on the wall. I went to crush it with my fist but as soon as i moved it just vanished.
You can actually try to bring these hallucinations on yourself before you sleep, its really simple you just lie on your back in bed, close your eyes for 5 minutes or so and then keep them open for a while, then close them, then open them until you really really feel drowsy. (Sometimes you will feel like you are on a rollercoaster, going up and down. You can actually feel the movement, its quite relaxing) When you feel as if your about to go to sleep, open your eyes. Sometimes you may hear things (Ive heard voices - That ALWAYS creeps me out!!!!) and you'll probably start to hallucinate. you'll either then fall asleep or become afraid of what your brain thinks you are seeing.
Interesting - it mentions feeling a presence when you are in this state.