Only that i know is that demons are made by fear. Some kind of anti-mater.
Barionic (light) mater is made by gravitation, by unification, by love. Demons are made by fear, by devision, by anti-gravitation.
They are not visibles by eye be cause our eye can see only the light.
They are feed by fear, and hurt by love.
So if you have deal with it, you must to know that its just some beings like you, who knows suffering (much more suffering, they even take delight in it) and want just to be happy, to survive, to exist.
They just want exist, this why they make us fear sometimes, because in this fear they exist, by this fear they feel their existence.
Feel compassion to them.
Sabbe dhamma anatta.