When my sister first brought home our rescue cat, he stared into space for what seemed like the entire night, and I don't think he slept for a single minute. Considering that Sesame is a black cat, I was convinced that this was definitive proof that my sister's apartment was haunted. But as it turned out, Sesame's behavior was completely explainable — and is actually very common. According to two vets, Dr. Carlos Gutiérrez, DVM, a small animal specialist, and Wendy Zimmerman, DVM, CVA, CCRP, the associate veterinarian at RAU Animal Hospital, there are four main reasons cats stare off into space (and none of them is because they're seeing spirits).
Dr. Gutierrez and Dr. Zimmerman both agree that staring into space is completely normal behavior in a healthy cat, but there are always exceptions, and it's always safest to consult your vet if you're concerned. If your cat is doing most of their staring at night and you think it goes beyond their nocturnal instincts, Dr. Gutierrez recommends paying close attention to their behavior all throughout the day, because "there could be an extenuating physical condition that's causing them to stay up at night." And Dr. Zimmerman reiterated, "If there are any possible symptoms that your cat could be losing their vision, such as bumping into things for example, you should take your cat to the vet right away." In most cases however, the vets reassured us that a cat staring at "nothing" is just a curious cat — and probably not because of ghosts.