Can anyone explain this weird behavior my cat exhibits?

So, for the past week my cat has been having this weird habit. After I head upstairs for bed, she will sit on one of the end tables downstairs, face the wall and just stare at it. And it’s at the same exact spot almost every night. She doesn’t do it all night, because she eventually comes up and sleeps on my bed. It is a little creepy.

Why would she do this? She’s about 5 years old and doesn’t like other cats too much (we have a couple). Medically she is pretty fit, a little underweight, but nothing to be worried about.

Anyone else have a cat that does something similar?