To wake up and find you mysteriously have a knackered arm
"ahh shit i must have been sleep wanking all night"
by TMB June 17, 2003
The act of wanking prior to sleep, so as to improve the quality of your rest and also have an excuse to think of unfuckingbelievably hot chicks.
Griigor: I should have my good sleepwank and a nap.
by AnimusNine April 28, 2009
The art of having a wank whilst sleeping.
"I had an awesome sleepwank last night dude"
by Pik0r June 17, 2007