What is difference between nervousness and anxiety?

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What is the difference between “Normal Stress” and an “Anxiety Disorder”? 

To be alive is to experience “stress“.   We are living in an age of rapid communication, endless to dos and limited down time.  It is inevitable to experience some moments of feeling on edge, overwhelmed, and unsure if we can cope with the pressures placed upon us.  In fact, if we did not experience any stress, we would lose our ability to survive.  If our ancestors did not experience stress at the site of a snake slithering towards them, they would not have reacted and fled for safety. But when does stress shift from being adaptive to being crippling? In general, one has entered the realm of anxiety disorders when:
You feel constantly tense, worried, or on edge
Anxiety interferes with your work, school, or family responsibilities
 You experience frequent fears that you know are irrational, but can’t shake
You believe that something bad will happen if certain things aren’t done a certain way 
You avoid everyday situations or activities because they cause you anxiety
You experience sudden, unexpected attacks of heart-pounding panic You feel like danger and catastrophe are around every corner