Phantom dog

This has occurred so often lately that I hesitate to post it. Perhaps my mind is simply playing tricks on me. It seems I'm frequently tripping over phantom dogs. This house is not especially light even in the middle of a sunny afternoon. The nature of this old pre-civil war structure is simply dark. I was upstairs, it was growing late and the sun was low in the sky so the upstairs main hall was receiving light only from its southernmost end. The rest of the hall was gloomy but not yet dark. I had just left the master bedroom, having changed my clothes, and headed down the hall toward the rear stairs. I almost rear ended a dog, schnauzer by appearance, who ran ahead of me down the hall and literally disappeared when it reached the lit end of the hall. Caught totally off guard I thought it was my little male schnauzer before realizing my dogs were both blocked from coming upstairs except at night. This schnauzer disappeared in the lit portion of the hall which would not have happened to a real dog. When I went down the rear stairs the gate was still up and both of my dogs were in the kitchen. It seems that dogs have replaced footsteps as the most common phenomena that we encounter here. I wonder what will be next. I really wish I could get a photograph of one of these "dogs", but it happens so fast and I never have a camera handy; but I'd probably still not react fast enough as the episodes are over in a matter of seconds.By the time I realize something strange has occurred it is over.