The process of self-pleasure followed by a nap.
After a hard days work you arrive home and find your day is incomplete. Therefore you have a wanknap - taking a mere half an hour. Afterwards you are recharged and reinvigorated.
the ability to have a wank, or "work the gerkin" in bed, proceeding sleep. This happens when one is still holding ones todger. You fall asleep whilst holding your cock on!
I'm tired, yet horny...I think I'll have a wanknap XD