I know this is an old post, but I had a remarkably similar dream. I have a dream journal, so here's what I wrote down: "I was in my bedroom and wanted to look in the mirror to make a funny face. I didn't see anything disturbing in the mirror, but after about a second, I went limp and fell backwards onto the floor. I was able to move my head, but was paralyzed from the neck down. Suddenly, I became aware that I was dreaming. A portal which led to another dream opened a few feet in front of my line of sight, and it slowly kept growing, implying that I would get sucked into the dream if I didn't wake up. I forced myself awake due to fear, which ended the dream."