The act of unknowingly masturbating while sleeping, often to the discomfort of your bed partner. Not usually remembered the following morning.
Lady: Sorry I couldn't help you out last night... I had a headache.
Dude: Whaddaya mean?
Lady: Oh, you don't remember? You woke me up three times last night, you were sleepturbating.
Dude: Oh, I'm sorry. I had no idea.