Phobia
We can define a special kind of fear or dread. The word phobia comes from the Greek phobos, the god of the same name that caused panic in his enemies. Therefore, in antiquity the term meant fear or terror, and so it was understood to almost the present day, when given a more specific use, separating it from other types of fear.
What is “special” this kind of fear, unlike fear and we all felt at some time, are these four qualities:
- It is a fear disproportionate to the situation that causes it.
- Who suffers recognized as absurd, without reasonable explanation.
- We have no control over it.
- Bring to avoid situations in which it appears.Being a form of fear, it is logical that the symptom common to all phobias are anxiety, palpitations, sweating, feeling of emptiness in the stomach, muscle tension, hypertension, tremor, etc … except in a type of simple phobia (blood-injection-injury), which is a syncope (dizziness, hypotension).
Source
Theories to explain why and how there are many phobias. This fact simply indicates that we can not answer this question today. What we can say is that there are factors associated with its development and maintenance.