I have an odd condition called sleep paralysis which puts me in a state of sleep, except for the actual sleeping part. So basically I'm almost completely paralyzed (like in REM sleep) except I can blink and breathe, but I can see around me and also hallucinate and hear things. Whenever I manage to get back to sleep properly after I experience this, I always end up in a lucid dream. It's great, I'll usually be in a nearby location, i.e. my street, but know perfectly well that I'm paralyzed in bed. I have complete control and there are plenty of inception like projections around to, well, do what I please with. Ahem. I have an almost 100% track record of getting into this state by waking up early (and still tired,) engaging my brain (maybe by watching an hours worth of whatever I fancy) and then trying to get back to sleep. So yeah, sleep deprivation does it.