What's up with my cat?

My cat Stalker use to lay down and lightly react to sounds and smells, you know the ones that everyone can smell. But lately she's been doing it more, to thinks that aren't even there. Even to the things that aren't even there that I'm aware of anyway. She also does it more violently, She'll practically throw her eyes open like something scared her. I won't move, I won't speak, Won't laugh, and she'll still do it. Sometimes she'll open her eyes and leave really quickly. This only happens when she's in my room. Is that something I should take as a warning or just brush it off?