Fear is an emotion and a normal reaction to a danger, it is often accompanied by an increase in heart rate, tremor and breathing difficulties. Fear depends largely on personal experience and can also be exacerbated or linked to an apprehension of particular situations (e.g. fear of animals, birds, snakes, spiders or enclosed spaces, etc.) and, in this case, we talk of phobia. When fear manifests itself irrationally and persistently, it can be an expression of an anxiety disorder.