I've experienced this a couple times but the most usual case is that my sister is watching tv while im asleep. because i remember a dream from a couple years ago where i had a dream i was in a horribly messy house and then i picked up a pink hello kitty toaster then someone came up from behind me and told me it made the face of hello kitty on the toast. i then woke up looked across the room at the my sister sitting in a chair (i slept in the living room that night.) then i looked at the tv and saw one of those shows where people come and help clean the house and sell stuff and one of the things i saw was a pink hello kitty toaster. i was puzzled and asked if that toaster made hello kitty's face on the toast. she looked at me weird and said "yeah, how do u know?" i told her the show effected my dream but she called me a liar.

But the most severe case i remember where i was sitting on my back porch and suddenly water filled the air and i was drowning. i began blacking out and i suddenly woke up, and threw my had back quickly. i then realised my hand got in the perfect position in front of my face so that the back of my hand plucked my mouth and nose stopping me from breathing.

Sorry about it being long and me rambling, but has any one else experienced this, and does anyone know why this sometimes happen?