Hey-
Yeah, I get movements out of the corners of my eyes. It's most easily compared to a shadow or something that quickly sped by. I doubt there is really much you can do. Just don't move your head every time it happens to look or others may think something is seriously wrong. This phenomena is pretty common, especially at night. Just wondering if you also have any problems with false motion directly in your field of view. This morning, I was walking out of a dark park towards street lights and the trees seemed to move as if the wind was blowing. Well of course I stopped and checked, there was no wind. Alittle odd, but my vision is not spectacular and my own movement contributed to the illusion.
If you become paranoid or anxious when manic, these slight movements will probably compound noticeably. I wouldn't worry unless you see something completely ridiculous.