I read in Why we sleep by Matt Walker that in your sleep, your brain starts experimenting with making connections between concepts it wouldn't make while awake, i.e. when it's job is to navigate the real world using logic and sanity (and that apparently is one of the proposed explanation for why dreams get so weird, illogical and random). In the book, he also writes about Thomas Edison's method for recording the dream induced ideas and novel connections of concepts. Edison would sit in the chair with three metal balls in his hand, the arm on the armrest, such that the hand with balls was hanging off the chair. Directly underneath that hand he would place a pan. Once he fell asleep deep enough to start dreaming, his muscles would relax, release the balls that in turn would make a noise hitting the pan, waking Edison up, giving him the chance to write down whatever he was dreaming about.

I don't know if you can actually use the technique, but I thought I'd share.

Edit: typo