Did i see my dead dog's ghost?

i have seen things "out of the corner of my eye" also pets, people and other things. In my case I think i has to do with poor peripahal vision. WHen we are tired or just waking up our periphal vision does not always work like it should. There is a small area where your eyes temporarily can't focus. Your brain fills in the blank with something you subconsiosly want to see.