What is fear? It can be many things. It is the uneasy and painful emotion that is caused by a sense of impending danger. It is the state of being alarmed or dreading something occuring in the future. It is anxiety toward the safety of a valued person or thing. In fear is the sense of worry over what might yet happen, of ambush, and disastrous possibilities. A lack of understanding allows the imagination to blossom and fill the instance with a thousand wild possibilities - once you understand the rules of the game, there is less to fear, as the possibilities are pruned away.
It can be seen in the face by the sudden widening of the eyes and/or mouth, often with the eyebrows raised, and sudden pallor. The frightened individual may hold their breath (or breath faster) and go motionless (or flee). They may crouch or cringe away from the object of their fear. Heart rate increased, muscles tremor, pupils dilate, neck muscles contract, and the voice may fail the frightened person.
Fear can be regarded in many ways by different people. It can be seen as a commodity. People can buy and sell fear - from thugs on the street to debt collectors to marketers for drink driving campaigns. It can be seen as weakness for those who see fear as a disabling emotion that makes you inferior to the object that causes fear. It can also be seen as a clever warning device that keeps you safe by alerting you to potential hazards. Some find it so debilitating that they avoid all mention or thought of it - walling up their fears in the belief that it is in their best interest to dam the sensation. For some, fear is the spice of life. It keeps them on edge, on their toes, and excited. What beliefs does your character hold about fear?
I would argue that fear is not, in and of itself, an enjoyable emotion - positive emotions can be caused by otherwise frightening occurences but those responses are excitement, anticipation, and perhaps certain kinds of anxiety. However, the afterglow of fear can be a powerful intoxicant as relief mingles with a sense of achievement mingles with the heady hormonal mix of adrenaline and even endorphins.
How does your character respond to fear? And what other responses do you think are possible?