Paranormal-- Shadow People

You see him there out of your peripherals a black form, a shadow. He transforms into a man that is void of all color and light, it happens right before your eyes. You turn your head and he stares into your eyes studying you before he vanishes into thin air...

We have all had similiar encounters, there are many scientific and logical explaination for why we see frieghtening shadows out fo the corner of our eye.  We can't all have a mental illness, or can we?