Most men can’t imagine how a woman could have an orgasm during rape, but theologists for some reason have always had something to say about experiencing pleasure in rape. Also, there is a share of women who have rape fantasies, even if one would need to look extremely hard to find one who would seriously want that to happen.
Saint Thomas Aquinas believed the sinfulness of dreams or lack of it depended on what happened before the night fell. In my humble opinion, there are some problems with his logic (if you watch a downright porn movie, you regret and confess, you are absolved, you get a wet dream - is it a new sin? - the old sin of watching that movie is already a past sin, so it isn’t in the light of the passage about past sins producing results in the form of dreams being had in the present, but without confession in the middle, it would seem to be a separate new sin of that sinful dream, so finally is it a part of the past sin or is it a separate new sin? - there is a problem here ), but it seems to point out in the right direction. However, exposing oneself to the possibility of such a dream by watching a movie is hardly the same as willingly procuring such a dream, so I can’t really see how one could make a separate sin out of the dream itself.
There seems to be a problem with sexual sensations going on when someone starts waking up. Obviously, if it can’t be controlled, there can’t be a sin in it going on, even if feeling of guilt will appear. But if it can be controlled, I can’t say how much of resisting and fighting is enough. And, obviously, there must be a difference between struggling and not struggling with it.
However, I may be wrong. I’m not a theologist and I may be tainted by may secular law studies when it comes to guilt and responsibility.