The Cat Heaps - Is She Sleeping?

My girlfriend and I moved into a bigger place about a week ago. About three nights ago we both started noticing odd behavior from our older cat. We both woken up to her with her hair raised, hissing at the empty hallway. The next morning my girlfriend and I had to be up early because she kept waking up off and on to footsteps down the hallway. She described it as boots on wood flooring. Last night I finally heard it myself. I woke up to the cat hissing and heard what sounded like someone pacing up and down the hallway for what felt like 10 minutes. Not sure exactly what's going on or whatever it is it's extremely active and has been for the