"What triggers that feeling of being watched?"

[bindeweede]

A short but interesting article about "blindsight", a term first coined in 1974. It is "the phenomenon of patients who were still able to respond to visual stimuli despite losing all conscious vision due to destruction of the visual cortex."

https://mindhacks.com/2017/05/26/what-t ... g-watched/

So when you’re walking that dark road and turn and notice someone standing there, or look up on the train to see someone staring at you, it may be your nonconscious visual system monitoring your environment while you’re conscious attention was on something else. It may not be supernatural, but it certainly shows the brain works in mysterious ways.