Odd Presence & Mystery Cat

On two occasions I have noticed a white cat with a black bib (almost like the reverse of tuxedo cat colouring), in the kitchen. It's not an old house & only one family has lived here since it was built a few years ago. When I saw it the first time I was doing the dishes at the sink & looked towards the doors to see the cat sitting there looking at the glass door. When I saw it, it seemed so normal & unremarkable like it was always there. Except when I looked away it registered a moment later what I'd seen. I looked back to find it gone.

Yesterday I was in the kitchen again & looked towards the dining table to see one of my cats on the table, & the same white cat with a black bib under the table. Again, it only registered a couple of seconds after looking away that I don't have a cat like that & in fact have never seen such a cat in the area or in life. It is so weird how it doesn't register in my head as not being out of place while I'm looking at it but only when I look away does it hit me like a ton of bricks what I just saw. I also feel sometimes in this house like I go from being alone in the room, to there being a heaviness in the air that is almost painful. I'm not sure what to make of it & I have never really considered ghosts before I came here. I always reason them away & I can't seem to do that now. My gut tells me it's really there.

Another weird thing is that my dogs & cats occasionally look into a space in the room at random & appear to either follow something or stare intently. Both my Staffy & my Husky dogs have growled at something in mid air recently & won't stop doing so until it appears to leave. It really does creep me out & I've been feeling somewhat ill when this presence comes into the room I'm in. My head hurts & my limbs feel heavy. Any advice as to what this may mean?