Fear, pain, and stress are almost synonymous. They are all resistance to what reality is right now. They are all ways for us to interpret the experience we are having in that moment as something that should not be. They are all defensive modes of being that are actually there to protect us. Think about it yourself. Don't take my word for it.

Think about you own experience of fear. What is it really? What does it come from? What is the relationship with pain? What is the relationship to stress?

Here is an excerpt from my book, "What Is Really Good?" on the topic:
The root of all stress is fear. Of course fear is a survival instinct. It is imprinted on the design of your ego (your sense of 'I') to motivate you to take protective action.

This is true for both physical and mental stress. Physical stress is
physical pain; subtle or blatant. It is a signal that something is wrong and to remove yourself from the situation. Mental stress is mental pain; subtle or blatant. It is a signal that the situation does not meet the ego's definition of well being. In both cases fear is the motivating factor that brings the signal of stress/pain.

Physical fear is always short lived and only comes from a direct physical threat. Mental fear is the real issue. It is at times mistaken for physical fear and it is actually over 99% of the fear you experience. The fear produced by your mind attempting to keep the ego and its many identifications in a state of well being is produced at disproportionate and dysfunctional levels.

Fear is supposed to keep us safe. Problem is, it has gone way past doing for us what it does for the animals. A wild animal gets scared; they fight or take flight. Then it is complete. A person fears about the future and stresses about the past. A person holds on to fear like a ball and chain.

Ironically, the fact that the animal doesn't hold on to the fear after the cause of it, is the same reason that we are so much more advanced. Their minds can not hold the ideas and concepts that ours can. As a result, their egos can not identify with ideas as ours can. Their only sense of identity is their physical selves and maybe offspring. Our egoic identity spreads as far as our concepts and ideas can take us. My stuff, my money, my house, my country, my business, etc. Our fear is magnified by the identifications.

To live without fear; live without stress; and minimize all physical pain is not as far off as you might think. As a matter of fact, you hold the key right now. It just needs some attention.