Little black dog reappears.

I was in the bathroom, at the sink, when I again observed a small black dog which I immediately thought was my younger dog, come into the bathroom and trot toward the far wall. I may have blinked, but I didn't see it disappear, but it did. My dog, we call "Shadow" was definitely downstairs at the time. I definitely saw this small, fuzzy, black dog for several seconds. I'm getting old; perhaps it was a hallucination. I'd hate to think so. This is the second such episode. We did observe a small white with brown spots dog when we first moved here and for several years thereafter but was a jack Russell type and hasn't made an appearance in some time. I'm just reporting the episode. I have no answers.