I don't this tread is by all means too old to respond. A lot can still be learned and new information can be brought to the table long after the final post.
Shadow people, corner-of-your-eye phenomena are quite common and something I certainly do not think is worth worrying about. IME I find the more highly strung, stressed out, sleep deprived or anxious one is, the more one experiences such unusual occurrences. I think it's a good way to acknowledge that you may need to do some personal adjusting; re-hydrate, sleep properly, get some nutrients, sunlight etc.
In the past, my girlfriend had experienced strange occurrences like this quite regularly as she was coming off SSRI's - always seeing shadow like people out of the corner of her eye, sometimes waking up in the middle of the night because she could
see that there was a person standing in our bedroom (complete hallucination). They were horrible, horrible meds to come off - bad side effects lasting many months
I am a piece of knowledge-retaining computer code imitating an imaginary organic being.