Why are people so afraid of the dark?

a need to switch on lights;
not wanting to go out at night;
symptoms like increased heart rate, increased sweating, tremors, and feeling worse.
Thus, fear of the dark is a fear of the unknown. We can’t see in such conditions, because of which our imagination can play out. And for us it is not predators, as for our ancestors, but non-existent monsters under the bed.