system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we get that feeling were being 'watched' or 'followed' in a dark room and similar places?

It just doesn't make sense, everyone knows that feeling and you start to get scared which leads to freaking yourself out and I don't understand how it works because there's never anything there.
gpt
Your body doesn't like darkness because it can't see well. So it tells you to be cautious, because something might be out there. If it's wrong, there's no harm. If your body doesn't make you cautious and it's wrong, you could die. So your body will err on the side of caution and make you think you're being followed, because that's more likely to keep you alive.