A mix between the feeling of fear and concern. In other words, it is a 'fight or flight' response to the built-in alarm to the perceived threat, whether real or imagined. The literal meaning of the word anxiety is 'to trouble' or 'to vex'. Anxiety is a mood condition, which often does not have identifiable triggering stimulus. The difference between fear and anxiety is that, it is fear when one is worried about a specific danger and anxiety is when one is worried about unspecific and objectless things, for no apparent reason.

http://www.maxmusclestack.com/alpha-xtreme