Your emotional and physical reactions to fear and anxiety are initiated by a series of chemical reactions deep inside your body. When you are fearful or anxious about something, for example a medical procedure, your system perceives it as a threat and swings into action. The human body goes into emergency mode, known as the “fight or flight” response, where energy and resources are diverted from general maintenance to deal with the danger. It is an instinctive reaction that floods your body with hormones such as cortisol and adrenalin to increase heart rate and blood pressure, boost the volume of sugars (glucose) available for fuel, and divert blood to major muscle groups. At the same time essential bodily functions that are not particularly useful in an emergency situation, such as reproduction and digestion, are temporarily slowed down.