What is fear?

There is the famous Mazlow’s hierarchy of needs that starts with breathing, food, and other physiological needs and ends with self-actualizations. Are fears rooted in satisfying our physical needs? Is there are hierarchy of fears, too?

I’ve heard many people say they feel empty, like they have a hole inside themselves which they don’t know how to fill. Is this just an extension of hunger?

Is fear an absence of love?