Fear in cats can be caused by many of the reasons which affect shy cats, along with a collection of more exact causes.
An imperative point for dealing with fearful cats: Do not stare unswervingly into your cats eyes when trying to calm him/her. A straight stare is a sign of aggression among cats and will only intensify his/her fears.
Unless your cat was born in your home, you have no way of truly knowing what his/her relationship was with earlier humans in his/her life, other than the information given by a shelter or cat rescue organization. The cat may have an inborn fear of humans because of prior cruelty or desertion.
Your cat can be taught to trust people, starting with you, but it may be a slow procedure. Be sure to take it in tiny, diminutive steps, try to get rid of his/her other fears, and kitty set the pace. Ultimately, once he/she has learned to trust you, other people in your life may follow the same progression. Don't be taken aback though, if kitty remains a one-person cat for the rest of his/her life.
The archetypal situation here is when a timorous cat is trapped in a covered litter box by a governing cat. It is also a universal reason for litter box avoidance. The solution is to have litter boxes with an "easy out," as well as addressing the “Type A” cat with a redirection method.
Loud noises, such as parties, construction, and holiday celebrations involving fireworks, can be unusually frightening to cats. Since these events are known of in advance, it is wise to remove the cats to a safe, quite room until the celebrations have ceased
Disasters such as floods, hurricanes, tornadoes, and earthquakes give little advance warning. It is your duty to have a good plan in place so that you are prepared. Your plan should include an emergency evacuation kit, which needs to contain one or more natural tonics for stress. Once things are back to normal, you can set upon the route of easing your cat's fears.
If you are loving and patient, your cat will ok up to you and trust you to do what is best.