I think my cat might have something wrong with him?

My cat will like just sit in a corner & stare at the wall, like there will be nothing there but he just sits & stares, no shadows or anything. & he stares at walls like I'll walk into a room & he will just be staring at the wall. Today I went into the kitchen & he was standing on the table with his head down just looking at the table with his tongue out of his mouth & it's really scaring me, like I don't think it's normal for cats to stare at walls & stuff. & I'm wondering if anyone could tell me what is wrong with him? Because I'm getting a little bit worried. Like why would he be doing this? Is it normal? Should I take him to the vet?