In Rite of Spring by Andrew M. Greeley, page 10-11, he explains a phenomena many people experience, but not to the extent that this character does, and takes the reader through an episode. Here is the explanation:
You must understand that in addition to being the quietest of quiet men, I am strange in another way.
I see things and people that others don't see. I recognized this phenomenon in early childhood, when I would tell my parents or my playmates about people I had seen. Their shocked reaction quickly taught me to distinguish sharply between my "special" events and "ordinary" events.
The phenomena that happened long ago or will happen sometime in the future or are happening at some great distance now are easily recognizable as distince from phenomena that others can see. The best way I can describe them is to say that they are played on a videotape that seems to be either in front of or behind the tape of ordinary consciousness. I suspect that it was more difficult as a child to make the distinction, but I learned, under the pressure of circumstances, to recognize the difference quickly enough.
I don't ask you to believe that such events happen. I will be content for the purposes of this story if you accept as a given that I experience them as happening. Or think I do.
As a very young child, I had an "imaginary" someone/something I talked to. I was so young that I only know this from ancedotal evidence. Once my mother talked to HER mother, the family Wise Woman, about it. She listened in, and announced that I was talking to Jesus. Personally, I'm kind of sorry I can't remember what I was seeing/hearing when I did it from my own experience. I guess I, too, quickly learned to ignore whatever it was.