shortly before having this dream, i read a book that involved satan worship. so i'm sure that contributed in some way or another.

i remember it quite vividly, which is extremely rare for me.

I was laying on my couch one night when i must have dozed off. It felt as though I was awake but some things just weren't right. I didn't feel right. All of a sudden, I became aware of a very powerful 'dark' presence... for lack of a better description. I remember thinking that it was Satan himself. It seemed as though it was trying to take over my mind, so I began to fight back. I don't remember being scared. I knew that if I gave in, I would seemingly lose my mind and plunge into darkness. I grew tired of fighting and let it pull me in. I immediately began to feel as though I were sinking into my couch. It felt very real. I became frightened at the sensation and shot up into a sitting position. I 'woke up' shortly thereafter, although it never really felt like I was asleep...

It was weird. Before I let it pull me in, I told myself that it was just a dream and that nothing would actually happened if I relaxed. But after I gave in, I felt a very strong pull.

It happened about a year ago, and I still remember it very very clearly.
Can someone explain what the heck happened or what it may mean?

I don't know if there is a technical term for what you experienced, but I've experienced it myself---that feeling of being pulled downward as if some force or pressure is pushing you down into a spiral.

Since you were on a couch, I'm assuming that you were probably tired from a long day and wanted to relax and fell asleep. I've been overtired when I've experienced that sinking feeling. You may have been overtired and your brain was overloaded.