Do you ever see things out of the corner of your eye?

I usually don't. Occasionally I see a sparkling "tracer" because of my Bipolar Disorder, but that's about it. All day today, however, I've been seeing lights and dark figures out the corner of my eye. And let me say this: the dark figures are easily some of the scariest damned things I have ever seen. Or maybe it's just because they startle me.

A friend of mine told me that they have had similar experiences, and has since childhood. I tried to Google the phenomenon and turned up more results about ghosts and shadow people than I care to think about.

Is it possible that I just had a wicked, skull-busting migraine yesterday and my brain is still recovering? That's what I'm going with.