Very insightful, Marcia. Thank you.

Well, the most obvious explanation to me is that this was just a sexual dream, with the woman's orgasm really being your (mental) orgasm - the woman in the dream really being an aspect of yourself

The woman could also be your anima and the sex in the dream can represent an integration with the "feminine" part of yourself.

Or she could represent another part of you that you are just becoming familiar with.

Her physical appearance (racial, etc.) might also have some significance for you.

The other people who are alarmed at having someone else in their house sound like they represent parts of yourself that are shocked at your discovering something new about yourself. (Could also be related to the fact that the dream involves you being physically "dirtied" by the girl's orgasm.)

In dreams, a house often represents you, psychologically, so concern about what is happening in the house could symbolize a concern about what is going on in your mind.

Not being able to turn the lights on could have to do with part of you wanting to "keep things in the dark" - to keep repressing these things about yourself.

The scream could also be a warning not to try to uncover things about yourself too quickly.