Fear

is a very common emotion.

When the brain detects stress (anger or fear), the human body releases a hormone called adrenalin, or epinephrine, which then acts to increase heart rate, blood pressure, cardiac output and blood sugar. It stimulates the circulatory system and the sympathetic nervous system, so blood is diverted from other organs to the muscles, the breathing rate increases to bring more oxygen to the muscles and sweating increases to cool the muscles.

There is also a theory that the secretion of adrenaline also makes the time appear to pass slower so that we have more time to react to the situation.

The adrenal gland

The medulla secretes two types of hormones: adrenalin or epinephrine and noradrenalin or norepinephrine. Norephinephrine is very important in maintaining normal blood circulation and is used in medical emergencies to raise blood pressure. The cortex cannot be removed surgically without endangering the patient, while the medulla can.

Anxiety

Sigmund Freud thought anxiety was triggered when someone´s aggressive or sexual drives made them behave unacceptably.
Some believe that anxiety is learned when innate fears occur with previously neutral objects or events.

Phobia

There are three major types of phobias: simple phobias (the fear of a specific object), agoraphobia (the fear of open public spaces) and social phobias. Agoraphobia is much more often seen in treatment than any other type, but psychiatrists still think that simple phobias are more common.