Let me try to describe it in more detail.
I wake up, glancing around the area, somewhat confused as to where I am. I recognize the place I'm at but I can't readily think of where it is. Right off the bat I feel like something is wrong. It's an indescribable feeling. Just that nothing that is happening, nothing in existence is right, and that something bad is going to happen. I also feel sort of like the world, or objects are way, way to big, or small, or the wrong shape and size Or that I'm not the right size, in a world that great a deep and hollow and I'm lost... but at the same time claustrophobic, like something is bearing down on me. I feel like I'm sort of trapped inside of myself, yet looking at myself from far away, and an observer. All the while I usually am in a state of panic (well hid, if I'm around others.)
These episodes usually happen when I just wake up, but it's hard to say that's what I was doing before-hand, because when it happens I lose all perspective of what was going on before. Only what is going on right there in that state of mind exists to me. Almost like I have no memory.
I've talked to a lot of people about it, and I'm not the only person it happens to. They all have their own way of describig it, but it's always very similar to my own experiances. But I don't know if this is specifically what's going on for you.
Edit: I should add, that this feeling is sort of like some of the paranoia that can come with smoking marijuana.