Verb. and Noun.
The situation when, after coitus, two people, in that case one male and one female, lay still on their sides (also called spooning), in which the penis of the male person remains inside the female person's vagina, until it ultimately becomes flask and inert. When the two people fall asleep under the effect of post-coitus endorphin, that's where the term takes all its sense. Do not mistake with the similar term Sleeping Bag.
'' I had a fabulous time last night ! We had loveful sexual intercourse, and then we remained in a sleeping vag.''