Most people have fears of some sort, at some times in their lives. That is natural. But people who have a fear that stays with them constantly, or keeps coming back, are said to have a phobia. Phobias can be fears of certain places, certain situations or certain objects. Examples are:
Acrophobia - a fear of high places (tall buildings, mountain tops or high bridges);
Agoraphobia - a fear of large, open spaces;
Claustrophobia - a fear of closed-in places (elevators or small rooms);
Hydrophobia - a fear of water;
Zoophobia - a fear of animals.
Doctors treat people by helping them to remember the incident that produced the fear. - bigsiteofamazingfacts.com; wikipedia.org; phobialist.com