Shadow People are not Mysterious

My last job, I had a coworker who thought it was very mysterious that so many people saw shadow people. A shadow person is a threatening dark figure people occasionally hallucinate, usually during sleep paralysis or after taking too many antihistamines. Now that I think about it, this is not mysterious at all. A shadow person is the simplest possible threatening hallucination. It's basically featureless, and your brain has seen hundreds of dark figures before. If your brain is feeling a little dopey and it's decided to be scared, why won't it put one at the foot of your bed? That seems like the most natural thing it could do in that situation.