Fear is a biological response that mankind has been living with since the dawn of time, although the things we fear have greatly changed. It is one of the most primal feelings we develop as humans. Science believes it developed as an aspect of our survival instinct, helping them thrive in spite of roaming predators.
https://www.daily-stuff.com/science-of-fear/
It’s all in the brain
The famous “fight or flight” response is instinctive and it determines a human’s course of action when faced with a threat — fighting it or escaping it. Contrary to what you might think, this response is not only triggered by fear or negative emotions. Excitement and happiness can stimulate the brain in just the same way. So, why do we respond to fear and a surge of joy differently if the brain process is the same?https://www.daily-stuff.com/science-of-fear/