What was this, and what caused it?

[DaneClark]

The closest I've ever come to having a sleep paralysis-like experience was this time when I woke up in the middle of the night, still feeling very sleepy but still fully aware of the fact that I was in the real world instead of a dream world, and and having some sort of hallucination that someone had just sat down on my bed. This could be very important for figuring out a technique for me that would actually work, so I really need some insight on it.

[Xanth]

Experiencing things when coming out of sleep is completely normal.
My understanding is that it's kind of a leakage of your dream and physical reality merging slightly and temporarily.
I've been experiencing stuff of that nature for as long as I can remember. 
Because of it, I've grown accustomed to seeing strange stuff in my room at night.
I've never figured out how to use this sort of thing in order to project though.  Once you're awake, your physical reality stabilizes and the dream imagery goes away relatively quickly.

[Windwalker.]

What you describe is actually close to how I achieve most of my projections. What you describe is precisely why I use a ramp timer to gently awaken me periodically. Next time when you wake up in that twilite/hypnapompic state,  instead of fully awakening you should immediately try going back to sleep yet remain aware. I believe you are experiencing theta brainwaves which normally we are asleep during theta brainwaves or close to it. This entire phenomenon seems to lie in the theta brainwave state. Good luck!