Fascinating. Possibly. Next time that happens, try taking some pictures and see what comes up.If you'd like help dealing with this, go to
http://ghoststudy.com . They have a message board where ghost hunters can help you out. You can even post your pictures for others to see.Its my favorite ghost site on the net and they are very helpful. You may like to explore the site itself. They even have a section on Shadow Ghosts that you might find useful given that you thought you saw someone out of the corner of your eye.