TAKEN DIRECTLY FROM CNN:

The results: The first three groups all reported experiencing increased genital and psychological arousal, as well as higher “state” desire, compared with the neutral group. The group who engaged in unstructured fantasy had the greatest arousal.

That’s great news for all of us, but particularly for women, who often tend to experience sexual desire in response to the sex they’re already having. In other words, you may not feel quite so “into” sex in the beginning, but your desire and arousal grow as the interlude progresses.

 

http://edition.cnn.com/2012/11/05/health/kerner-fantasies/index.html?hpt=he_c2