Verb: The act of masturbating while in the midst of deep sleep. The person is not consciously aware of their actions and thus (whether dreaming about it or not) starts masturbating in their sleep. Similar to a wet dream in that it is completely involuntary and uncontrollable.
After spending the night with my friend, my shorts were soaked. I figured I just had a wet dream, but my friend told me that I woke him up because of my furious sleepurbating.