This happened to me several years ago and I still ponder it very frequently. This is not a dream, but an experience from my waking life...
I am watching t.v. in the basement. I am home alone and trying to nap. It is about 7pm. The basement is dark except for the glow of the television. I am watching the weather channel and it begins to flicker with static. With the remote I try changing the channel and all I am getting is static. I get up to check the input and as I approach I see something move in the corner behind the t.v. I am frightened. I leap back to the couch for safety. I peer into the dark corner and feel a gigantic presence. Flashes of glowing red and green reptile like talons, jagged sharp teeth, and snake like eyes is all I see. I feel like I am hallucinating. I can't make out any form of the body and all I see are these few features over and over again in flashes. It's getting closer to me and I feel paralyzed.
Without any control over it I begin to feel warmth in between my legs and then in an instant I am having full strength multiple orgasms. It was painful to go from an almost completely relaxed state of trying to nap to instantly having multiples. I am feeling completely invaded and cannot escape. I start sobbing. It was such a crazy sensation to feel like I was being raped and experiencing pain while simultaneously having orgasms. This went on for what felt like two hours before I fully gave up and stopped crying. I Surrendered to what was happening and began to identify with this being. I writhed and twisted and contorted my body in ways that seemed impossible. I became a viewer. I left my body. This went on and on. Then finally as swift as it came, it was gone. Just like that. I lay there still flopping a bit and covered in sweat. I feel myself enter back into my body and almost immediately feel sick. I crawled to the bathroom and puked until I was dry heaving. I gagged and gagged. It was so painful. When I had finally calmed down from this purge I stumbled to bed. It was 4am. I went to sleep.... two weeks later I found out I was pregnant with my daughter.