What is flight or fright?

I believe you are referring to the fight or flight reflex. when an animal is in a stress type situation( i.e being attacked by another animal)it will usually make the decision to either fight or run almost reflexively this is called the fight or flight reflex. note:this is my limited understanding of the fight or flight reflex.

But it happens to refer mostly to HUMAN 'animals'.

The reflex, per se, is the emergency reaction of the sympathetic division of the autonomic nervous system. It dumps sugar and cholesterol into the bloodstream, stops digestion, dries up saliva, causes the heart to race and the blood pressure to rise, and increases sweating and galvanic skin responses. Anger is the "fight" part, fear is the "flight" part. They are natural emotions.

In primitive times, this was necessary because humans often had to defend themselves with great vigor and energy. But some scientists today wonder if it is now more of a liability than an asset.

There are people whose autonomic nervous system does not function correctly, in some cases due to a basic problem with the brain and central nervous system.

Two psychiatric disorders have opposite etiologies: in Borderline Personality Disorder, a person's sympathetic nervous system reacts very strongly and far too easily. This can wear away at health and deplete strength. In Antisocial Personality Disorder (psychopaths, sociopaths), the SNS reacts sluggishly and cannot sustain enough energy to get the person through a real crisis before exhaustion sets in. Other illnesses, such as Parkinson's Disease and Addison's Disease, directly affect the adrenal glands, which are very important as part of the fight or flight reaction.