Back in '94 I had dreams of massively mutually recursive data structures after immersing myself in ML (a Lisp like language) for several days before an exam. The structures were a programmatic representation of Ministry's Psalm 69, an industrial metal track that was playing on my hifi/alarm and woke me after far too little sleep, at 7:30am. The whole auditory hallucination experience was very vivid, odd, and sadly hasn't happened since.

Not that we want to encourage sleep deprivation or other means of inducing hallucinations, but in one of his books, interaction architect Bruce Tognazzini alleges that if you eat a big cheesy pizza just before you go to bed, you've got a fair chance of having some 'creative' dreams.